Download 植物生物学（Biology of Plants）双语课程教案

植物生物学（Biology of Plants）双语课程教案
Botany: An Introduction
In the Introduction We’ll study the following topics:
•Evolution of Plants
•Evolution of Communities
•The Appearance of Human Beings
By the time you finish studying the introduction, you should be able to answer the
following questions:
1. What are the main factors thought to be responsible for the origin of life on
Earth, and what evidence supports the hypothesis that life arose in the ocean?
2. What is the principal difference between a heterotroph and an autotroph,
and what role did each play on the early Earth?
3. Why is the evolution of photosynthesis thought to be such an important event
in the evolution of life in general?
4. What were some of the problems encountered by plants as they made the
transition from the sea to the land, and what structures in terrestrial plants
apparently solve those problems?
5. What are bioms, and what are the principal roles of plants in an ecosystem?
Evolution of Plants
•Life Originated Early in Earth’s Geologic History
•The planet Earth is some 4.5 billion years old, evidence obtained by analysis of carbon
particles on the earth indicate that life already existed on earth 3.85 billion years ago.
•Evidence of the presence of life on earth as early as 3.85 billion years ago might mean
that life was eliminated and reemerged.
•Of the nine planets in our solar system, only one , as far as we know , has life on it. This
planet Earth, is visibly different from the others. From a distance, it appears blue and
green, and it shines a little. The blue is water, the green is chlorophyll, and the shine is
sunlight reflected off the layer of gases surrounding the planet’s surface.
History of Life
•The earliest known fossils from rocks in northwestern Western Australia, dated at 3.5
billion years of age.
•They are about a billion years younger than the earth itself, but there are few suitable
older rocks in which to look for earlier evidence of life.
The Chemical Building Blocks of Life Accumulated in the Early Oceans
1
•In the 1930s, the Russian scientist Oparin proposed that vast quantities of carbon- and
hydrogen-containing compounds were formed in the early atmosphere from volcanic
gases composed of methane, ammonia, water vapor,and hydrogen.
•Miller obtained a variety of complex organic molecules similar to those that form the
fundamental building blocks of all life.

Stanley Miller, while a graduate student at the University of Chicago in the 1950s,
used apparatus such as that shown here to simulate conditions he believed existed
on the primitive Earth. Hydrogen, methane, and ammonia were circulated
continuously between a lower "ocean," which was heated, and an upper
"atmosphere," through which an electric discharge was transmitted. At the end of
24 hours, about half of the carbon originally present in the methane gas had been
converted to amino acids and other organic molecules. This was the first test of
Oparin's hypothesis.
Another theory for the origin of the chemical precursors essential to life on Earth
points to comets as their source.
•The comet Hale-Bopp, seen here above Smith Rocks State Park, Oregon, in the spring of
1997, is made up of dirty ice that contains many of the chemical precursors of life. Some
scientists believe that comets falling on the early earth in vast numbers provided the
chemical “seeds” that give rise to the earth’s rich diversity of living organisms.
Most Likely, the Forerunners of the First Cells Were Simple Aggregations of
Molecules
•When dry mixtures of amino acids are heated at moderate temperature, polymers known
as thermal proteinoids are formed. Each of these polymers may contain as many as 200
amino acid subunits. When the polymers are placed in water solution and maintained
under suitable conditions, they spontaneously form proteinoid microspheres, as shown
here.
Autotrophic Organisms Make Their Own Food, but Heterotrophic Organisms must
Obtain Their Food from External Sources
•Heterotroph:living organism that obtains its energy from carbohydrates and other
organic material. All animals and most bacteria and fungi are heterotrophic.
•Autotroph: organisms that use inorganic substances as energy sources and carbon
dioxide as a carbon source.
•
•
•
A modern heterotroph and a photosynthetic autotroph.
(a) A fungus, Coprinus atramentaris, growing on a forest floor in California.
(b) Large flowered trillium(Trillium grandiflorum,大花延龄草), one of the first
plants to flower in spring in deciduous woods of eastern and midwestern North
American.
2
Photosynthesis Altered Earth’ Atmosphere, Which in Turn Influenced the
Evolution of Life
•The increase in oxygen level which resulted from photosynthesis had two consequences:
•Ozone in the out layer of atmosphere. By about 450 million years ago, organisms,
protected by the ozone layer, could survive in the surface layers of water and on the land.
•Increase in free oxygen, which was accompanied by the first appearance of eukaryotic
cells.
The Seashore Environment Was Important in the Evolution of Photosynthetic
Organisms
•The waters near seashore were rich in nitrates and minerals carried down from the
mountains by rivers and streams and scraped from the coasts by the ceaseless waves.
•Multicellular photosynthetic organisms were better to maintain their position against the
action of the waves and to anchor their bodies to the rocky surfaces.
•
•
•
A fossil of Cooksonia, one of the earliest and simplest plants known, from the
Late Silurian period(414-408 million years ago).
Cooksonia consisted of little more than a branched stem with terminal sporangia,
or spore-producing structures.
Multicellular photosynthetic organisms anchored themselves to rocky shores early
in the course of their evolution.
Colonization of the Land Was Associated with the Evolution of Structures to Obtain
Water and Minimize Water Loss
• Diagram of a young broad bean(Vicia faba)plant, showing the principal organs
and tissues of the modern vascular plant body.
Evolution of Communities
•Some examples of the enormous diversity of biological communities on Earth. (a)Fall
color in the eastern deciduous forest. Note the presence of a few evergreens among the
hardwoods.

(b)View of the tundra, locality unknown.
•(c) In Africa, savannas are inhabited by huge herds of grazing mammals, such as these
zebras. The tree in the foreground are acacia（刺槐）.
•(d)The tropical rainforest, shown here in Costa Rica, is the richest, most diverse biome
on earth, with at least two-thirds of all species of organisms on Earth found there.
3
•(e) Deserts typically receive less than 25 centimeters of rain per year. Here in the
Sonoran desert in Arizona, the dominant plant is the giant saguaro cactus.Adapted for life
in dry climate, saguaro cactuses have shallow, widespreading roots and thick stems for
storing water.
•Mediterranean climates are rare on a world scale. Cool, moist winters, during which the
plants grow, are followed by hot, dry summers, during which the plants become dormant.
Shown here is a pine-oak chapparal photographed on Mount Diablo in California.
California Wildfire in 2003
Ecosystem Are Relatively Stable, Integrated Units That are Dependent upon
Photosynthetic Organisms
•Biological communities, along with the nonliving environment of which they are part,
are known as ecological systems, or ecosystems.
•The stability of an ecosystem may be disrupted by non-human (Fire, flood) factors or by
human (Urbanization, pollution) factors. A large disturbance (Volcanic eruption or
prolonged drought) may alter or destroy an entire ecosystem.
Appearance of Human beings
•The clockface of biological time, which shows when important events in the Earth's past
would have occurred if the Earth's 4.5-billion year history were condensed into one day.
Life first appears relatively early, sometime before 6:00 a.m. on a 24-hour time scale. The
first multicellular organisms do not appear until the early evening of that 24-hour day,
and Homo, the genus to which humans belong, is a late arrival--at about 30 seconds to
midnight.
Plant Biology Includes Many Different Areas of Study
•Plant physiology:
the study of how plants function, how they capture and transform energy and how they
grow and develop.
•Plant morphology:
the study of the form of plants.
•Plant anatomy
the study of plant internal structure.
•Plant taxonomy and systematics
Involving the naming and classifying of plants and studying the relationships among
them.
• Plant cytology:
the study of plant cell structure, function, and life histories.
• Plant genetics:
the study of heredity and variation.
• Molecular biology:
4
the study of the structure and function of biological molecules.
• Economic botany:
the study of past, present, and future uses of plants by people.
• Plant ecology:
the study of the relationships between plant organisms and their environment.
• Paleobotany:
the study of the biology and evolution of fossil plants.
5
Chapter 1 Introduction to the Plant Cell
In this Chapter, we’ll study
•Development of the Cell Theory
•Prokaryotic Cells and Eukaryotic Cells
•The Plant Cell: An Overview
•Plasma Membrane
•Nucleus
•Chloroplasts and Other Plastids
•Mitochondria
•Peroxisomes
•Vacuoles
•Oil Bodies
•Ribosomes
•Endoplasmic Reticulum
•Golgi Complex
•Cytoskeleton
•Flagella and Cilia
•Cell Wall
•Plasmodesmata
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. How does the structure of prokaryotic cell differ from that of a eukaryotic
cell?
2. What are the various types of plastids, and what roles does each play in the
cell?
3. What are the principal components of the endomembrane system, and what
role does each play in that system?
4. What is meant by the cytoskeleton of the cell, and with what cellular
processes is it involved?
5. How do primary cell walls differ from secondary cell wall?
Cell theory
•All living organisms are composed of one or more cells;
•The chemical reactions of a living organism, including its energy-releasing processes
and its biosynthetic reactions, take place within cells;
•Cells arise from other cells;
•Cells contain the hereditary information of the organisms of which they are a part, and
this information is passed from parent cell to daughter cell.
Landmarks in Study of Cell Biology
•1595 Jansen credited with 1st compound microscope
6
•1626 Redi postulated that living things do not arise from spontaneous generation.
•1655 Hooke described ‘cells’ in cork.
•1674 Leeuwenhoek discovered protozoa. He saw bacteria some 9 years later
•1833 Robert Brown descibed the cell nucleus in cells of the orchid.
•1838 Schleiden and Schwann proposed cell theory.
•1840 Albrecht von Roelliker realized that sperm cells and egg cells are also cells.
•1856 N. Pringsheim observed how a sperm cell penetrated an egg cell
•1858 Rudolf Virchow (physician, pathologist and anthropologist) expounds his famous
conclusion: cells develop only from existing cells
•1857 Kolliker described mitochondria.
• 1869 Miescher isolated DNA for the first time.
•1879 Flemming described chromosome behavior during mitosis.
•1883 Germ cells are haploid, chromosome theory of heredity.
•1898 Golgi described the Golgi apparatus.
•1926 Svedberg developed the first analytical ultracentrifuge.
•1938 Behrens used differential centrifugation to separate nuclei from cytoplasm.
•1939 Siemens produced the first commercial transmission electron microscope.
•1941 Coons used fluorescent labeled antibodies to detect cellular antigens.
•1952 Gey and co-workers established a continuous human cell line.
•1953 Crick, Wilkins and Watson proposed structure of DNA double-helix.
•1955 Eagle systematically defined the nutritional needs of animal cells in culture.
•1957 Meselson, Stahl and Vinograd developed density gradient centrifugation in cesium
chloride solutions for separating nucleic acids.
•1965 Cambridge Instruments produced the first commercial scanning electron
microscope.
7
•1976 Sato and colleagues publish papers showing that different cell lines require
different mixtures of hormones and growth factors in serum-free media.
•1981 Transgenic mice and fruit flies are produced. Mouse embryonic stem cell line
established.
•1998 Mice are cloned from somatic cells.
•2000 Human genome DNA sequence draft.
Janssen's Microscope
•The microscope illustrated above was built by Zacharias Janssen, probably with the help
of his father Hans, in the year 1595
Robert Hooke's Microscope
•This beautiful microscope was made for the famous British scientist Robert Hooke in the
seventeenth century, and was one of the most elegant microscopes built during the period.
Hooke illustrated the microscope in his Micrographia, one of the first detailed treatises
on microscopy and imaging.
The Galileo Microscope
•Although this seventeenth century microscope has been attributed to Galileo, a close
inspection of the construction details indicates that it was made in the late 1600s, about
50 years after the famous astronomer-scientist's death.
COMPARISON OF CHARACTERISTICS
EUKARYOTIC CELLS
1.
Possess a true “nucleus”.
a.
Nuclear material surrounded by a nuclear membrane.
b.
Nuclear material organized into paired chromosomes.
c.
Nuclear material (DNA) associated with proteins called histones form the
chromosomes.
d.
Nucleus contains nucleolus - sites of ribosome synthesis.
A.
B.
PROKARYOTIC CELLS
1.
No “true” nucleus - nucleoid.
a.
No nuclear membrane.
b.
No paired chromosomes.
c.
No histones.
8
d.
No nucleolus.
2. Internal structure more complex - contains organelles - each have a specific
function.
3.
Cytoplasmic streaming - continuous movement of the cytoplasm.
4.
Cell membranes contain complex lipids - sterols (cholesterol).
5.
Cell walls
a. Occur only on plant cells, fungi
b. Composed of cellulose, chitin.
6.
Division occurs by mitosis, meiosis.
2. No organelles.
3.
4.
No cytoplasmic streaming.
Cell membrane contains no sterols.
5.
6.
Cell walls
a.
All typical prokaryotic cells possess cell walls.
b.
Composed of peptidoglycan (murein).
Division - binary fission.
Prokaryote. A single cell from a filament of cells of a photosynthetic prokaryote, the
cyanobacterium Anabaena azollae. In addition to the cytoplasmic components found in E.
coli , this cell contains a series of membranes in which chlorophyll and other
photosynthetic pigments are embedded. Anabaena synthesizes its own energy-rich
organic compounds in chemical reactions powered by the radiant energy of the sun.
Eukaryote. Chlamydomonas, a photosynthetic eukaryotic cell, which contains a
membrane-bounded nucleus and numerous organelles. The most prominent organelle is
the single, irregularly shaped chloroplast that fills most of the cell. It is surrounded by an
envelope consisting of two membranes and is the site of photosynthesis.
Eukaryote. A cell from the leaf of a maize plant. The granular material within the
nucleus is chromatin. It contains DNA associated with histone proteins. The nucleolus is
the region within the nucleus where the RNA components of ribosomes are synthesized.
Note the many mitochondria and chloroplasts, all bounded by membranes. The vacuole, a
fluid-filled region enclosed by a membrane, and the cell wall are characteristic of plant
cells. As you can see, this cell closely resembles Chlamydomonas, shown in Figure 3-4.
9
The Plant Cell: An Overview
•The plant cell typically consists of a more or less rigid cell wall and a protoplast.
• Protoplasm consists of a cytoplasm and a nucleus.
• The cytoplasm includes distinct, membrane bound entities (organelles such as plastids
and mitochondria), systems of membranes (the endoplasmic reticulum and dictyosomes)
and nonmembranous entities (such as ribosomes, actin filaments, and microtubules).
•The rest of the cytoplasm- the “cellular soup”, or cytoplasmic matrix, in which the
nucleus, various entities, and the membrane systems are suspended – is called ground
substance (cytosol).
•The cytoplasm is delimited from the cell wall by a single membrane, the plasma
membrane.
•In contrast to most animal cells, plant cells develop one or more liquid-filled cavities, or
vacuoles, with their cytoplasm.
•The vacuole is bounded by a single membrane called the tonoplast.
Structure of a typical plant cell
Membrane Structure and Function
The above figures shows the typical "Unit" membrane which resembles a railroad track
with two dense lines separated by a clear space. These figures actually show two
adjacent plasma membranes, both of which have the "unit membrane" structure.
Diagram of Danielli and Davson ’s early model of the cell membrane
•In the early 1935, Danielli and Davson studied triglyceride lipid bilayers over a water
surface. They found that they arranged themselves with the polar heads facing outward.
However, they always formed droplets (oil in water) and the surface tension was much
higher than that of cells. However, if you added proteins, the surface tension was reduced
and the membranes flattened out.
Diagram of Robertson’s model of the cell membrane
•In 1957 Robertson noted the structure of membranes seen in the previous electron
micrographs. He saw no spaces for pores in the electron micrographs. He hypothesized
that the railroad track appearance came from the binding of osmium tetroxide to proteins
and polar groups of lipids.
Basic Unit Membrane Architecture
•All membranes contain proteins and lipid. However, the proportion of each varies
depending on the membrane. For example:
•Mitochondrial inner membrane contain 76% protein and only 24% lipid.
•Plasma membranes of human red blood cells and mouse liver contain nearly equal
amounts of proteins (44, 49% respectively) and lipids (43, 52% respectively).
10
Fluid Mosaic Model of membrane structure
•It was proposed by S. J. Singer& G. Nicolson(UCSD) in 1972
•The membrane is composed of a bilayer of lipid molecules-with their hydrophobic
“tails” facing inward and large protein molecules.
•The proteins traversing the bilayer are a type of integral protein known as
transmembrane proteins. Other proteins, called peripherial proteins, are attached to some
of the transmembrane proteins.
•The portion of a transmembrane proteins molecule embeded in the lipid bilayer is
hydrophobic and the portion exposed on either side of the membrane are hydrophilic.
•Short carbohydrate chains are attached to most of the protruding transmembrane proteins
on the outer surface of plasma membrane.
•The whole structure is quite fluid, and hence the proteins can be thought of as floating in
a lipid sea.
Membrane functions
•selective permeability barrier (regulate molecular & ionic compositions of cells and
intracellular organelles)
•information processing (signal reception and transmission/transduction)
•organization of reaction sequences (e.g., electron transport)
•energy conversion
a) photosynthesis (light energy --> chemical bond energy)
b) oxidative phosphorylation (oxidation --> chemical bond energy)
Nucleus
•The nucleus occurs only in eukaryotic cells, and is the location of the majority of
different types of nucleic acids.
• Structure of the nucleus. Note the chromatin, uncoiled DNA that occupies the space
within the nuclear envelope.
•Structure of the nuclear envelope and nuclear pores
•The nuclear envelope is a double-membrane structure. Numerous pores occur in the
envelope, allowing RNA and other chemicals to pass, but the DNA not to pass
•Nucleus with Nuclear Pores (TEM x73,200). The cytoplasm also contains numerous
ribosomes.
• Lily Parenchyma Cell (cross-section) (TEM x7,210). Note the large nucleus and
nucleolus in the center of the cell, mitochondria and plastids in the cytoplasm.
The Function of Cell Nucleus
11
•The cell nucleus is a remarkable organelle because it forms the package for genes and
their controlling factors. It functions to:
•Store genes on chromosomes
•Organize genes into chromosomes to allow cell division
•Transport regulatory factors & gene products via nuclear pores
•Produce messages ( messenger Ribonucleic acid or mRNA) that code for proteins
Produce ribosomes in the nucleolus
•Organize the uncoiling of DNA to replicate key genes.
Chloroplasts and Other Plastids
•Plastids are organelles that occur only in plants. Their most prominent members are the
chloroplasts. Others plastids are the colored chromoplasts and the colorless leucoplasts as
well as their proplastids.
•Proplastids may differentiate into complete plastids during the development of the plant
embryo. Their ripening into chloroplasts occurs usually only after light exposure
•Plastids contain DNA that encodes some of their proteins (others are encoded by the
nucleus) and they reproduce by division. All of the forms of plastid are interconvertible.
• Much of fall color is the result of the transition from chloroplast to chromoplast in the
leaves of deciduous trees.
•This plastid from a young strawberry fruit is intermediate between a chloroplast
(presence of thylakoid) and an amyloplast (large starch grains).
Chloroplast: the site of photosynthesis
•Chloroplast contain chlorophyll, the green pigment necessary for photosynthesis to
occur, and associated accessory pigments (carotenes and xanthophylls) in photosystems
embedded in membranous sacs.
• Thylakoids (collectively a stack of thylakoids are a granum [plural = grana]) floating in
a fluid termed the stroma.
•Chloroplasts are usually diskshaped and measure between 4 and 6 micrometers in
diameter.
•Chloroplasts contain many different types of accessory pigments, depending on the
taxonomic group of the organism being observed
•The chloroplast is the organelle of photosynthesis. In many ways, the chloroplast
resembles the mitochondrion.
•1.Both are surrounded by a double membrane with an intermembrane space.
•2.Both have their own DNA .
•3.Both are involved in energy metabolism.
•4.Both have membrane reticulations filling their inner space to increase the surface area
on which reactions with membrane-bound proteins can take place.
Chloroplasts and endosymbiosis
•Like mitochondria, chloroplasts have their own DNA, termed cpDNA.
12
•Chloroplasts of Green Algae and Plants (descendants of some Green Algae) are thought
to have originated by endosymbiosis of a prokaryotic alga similar to living Prochloron
(Prochlorobacteria).
•Chloroplasts of Red Algae are very similar biochemically to cyanobacteria (also known
as blue-green bacteria ). Endosymbiosis is also invoked for this similarity, perhaps
indicating more than one endosymbiotic event occurred.
Chromoplasts Contain Pigments Other Than Chlorophyll
•Chromoplasts are pigmented plastids, which lack chlorophyll but synthesize and retain
carotenoid pigments.
•Of variable shape, chromoplasts are often responsible for the yellow, orange, or red
colors of many flowers, old leaves, some fruits, and some roots,such as carrots,
•Chromoplasts may develop from previously existing chloroplasts by a transformation in
which the chlorophyll and internal membrane structure disappear and masses of
carotenoids accumulate, as occurs during the ripening of many fruits.
Capsicum (Red Pepper) Fruit Tissue
Chromoplasts from Marigold Flowers(right).
Leucoplasts Are Nonpigmented Plastids
•Structurally the least differentiated of mature plastids, leucoplasts lack pigments and an
elaborate system of inner membranes.
•Leucoplasts are non-pigmented plastids involved in either synthesis or storage, there are
three types:
•Amyloplasts - colorless plant organelle related to starch production & storage
•Aleuroplasts - colorless plant organelle related to protein production & storage
•Elaioplasts - colorless plant organelle related to oil & lipid production & storage
•Commercial slide of Amyloplasts that store starch. These are the famous amyloplasts of
the "Irish" potato which actually originated in the Andes(left).
•Unstained amyloplasts from Potato. Note the striations due to the highly organized
starch deposition(middle).
•The Amyloplasts from Cana are hard to see with normal bright field microscopy(right).
•Leucoplasts in Zebrina(吊竹梅） Leaf Cells
•Leucoplasts clustered around the Nucleus of a Parenchyma Cell stained with Toluidine
Blue.
Mitochondria
13
•Mitochondria contain their own DNA (termed mDNA) and are thought to represent
bacteria-like organisms incorporated into eukaryotic cells over 700 million years ago
(perhaps even as far back as 1.5 billion years ago).
• They function as the sites of energy release (following glycolysis in the cytoplasm) and
ATP formation . The mitochondrion has been termed the powerhouse of the cell.
• Mitochondria are bounded by two membranes. The inner membrane folds into a series
of cristae, which are the surfaces on which ATP is generated.
•Outer membrane - contains transport protein (passes molecules up to 5K).
• Inner membrane - very selectively permeable
•Cristae - inner membrane holds respiratory assemblies of ETC
• Mitoplasm - "matrix" aqueous compartment - DNA, ribosomes, etc.
•Shape and size:elongate cylinders to oblate spheroids. 3-5 um long by 0.5-1.0 um dia,
"shape-shifters", mobile.
•Number : 20 to 1,000 per cell ; greater in more active cells; can make-up as much
as 20% of cell's volume.
• The structure of mitochondria and Note folds in the inner membrane forms the "cristae".
Mitochondria and endosymbiosis
•During the 1980s, Lynn Margulis proposed the theory of endosymbiosis to explain the
origin of mitochondria and chloroplasts from permanent resident prokaryotes. According
to this idea, a larger prokaryote (or perhaps early eukaryote) engulfed or surrounded a
smaller prokaryote some 1.5 billion to 700 million years ago.
•Instead of digesting the smaller organisms the large one and the smaller one entered into
a type of symbiosis known as mutualism.
Peroxisomes
•Peroxisomes(microbodies) are spherical organelles that bounded by a single membrane
and range in diameter from 0.5 to 1.5 micrometers.
•Peroxisomes possess neither DNA nor ribosomes, but now they are believed to be selfreplicating organelles, like plastids and mitochondria.
•Membrane sac contains enzymes for metabolizing waste products from photosynthesis,
fats and amino acids. Hydrogen peroxide is a product of metabolism in
peroxisomes. Catalase, which breaks down the peroxide, is also present and serves as a
marker enzyme for these organelles.
•The left Electron micrograph shows part of a cell from Arabidopsis thaliana （拟南芥
菜）, with a chloroplast, peroxisome and mitochondrion in close juxtaposition.
•The right Electron micrograph showing a peroxisome (p) closely appressed to two
chloroplasts (c) and a mitochondrion (m) in a tobacco leaf cell. （From Huang, Trelease
and Moore. 1983. Plant Peroxisomes）.
14
Vacuoles
•1. Together with plastids and cell wall, the vacuole is one of the three characteristic
structures that distinguish plant cells from animal cells.
•2. The Vacuole is a large membrane-bounded sac(tonoplast) that takes up a large
amount of space in most Plant Cells.
•3. The vacuole serves as a storage area, and may contain stored proteins, ions, waster,
anthocyanins or other cell products.
•4. Vacuoles of some plants contain toxic secondary metabolites, such as nicotine and
tannin that discourages animals from eating the plant's leaves.
•5. Cells of Animals and other organisms also may contain vacuoles, but they are much
smaller and are usually involved in FOOD DIGESTION.
•6. Vacuoles are also involved in the breakdown of macromolecules and are comparable
in function with the organelles known as lysosomes that occur in animal cells.
7. The vacuole may originate directly from the endoplasmic reticulum, but most of the
tonoplast and vacuolar proteins are derived directly from the Golgi complex.
8. The vacuole is often a site of pigment deposition.
•Plant cell central vacuole(left).
•Druse Crystal seen with Bright Field Illumination(middle)
•Raphides in an isolated Vacuole seen with crossed Polarizers
(right)
•Electron micrograph of a "typical" Parenchyma cell. Note the large central vacuole, the
peripheral cytoplasm with well developed chloroplasts and the relatively thin cell wall.
•Later stage in the development of a storage parenchyma cell from Pinus cotyledon. Note
the vacuolation due to the breakdown of storage lipids and proteins (PB = Protein Body).
Oil bodies
•Oil bodies, or lipid droplets, are more or less spherical structures that impart a granular
appearance to the cytoplasm of a plant cell.
•Oil bodies are widely distributed in plant cells and abundant in some fruits like peanut,
sunflower,sesame, and so on.
•Oil bodies , often incorrectly described as organelles(spherosomes), are thought to arise
in endoplasmic reticulum, but they are not bounded by a membrane.
•Oil bodies and cell walls of Scapania scandica in Oregon(left) . Median cells (left,
imaged at 400x) and marginal cells (right, imaged at 1000x).
•Many, but not all, liverworts have oil bodies. While the function of oil bodies is not
clearly known, they can be very useful characters when identifying species and genera.
• Lipid bodies stained with Sudan. Some cells may contain large amounts of storage
lipids in vacuoles large & small. These stain red with Sudan III
•Storage Parenchyma cell from Pinus cotyledon. The Vacuole (V) is being formed by the
metabolism of the storage lipids. N=Nucleus.
Ribosomes
15
•Ribosomes are small particles which are not membrane-bounded and thus occur in both
prokaryotes and eukaryotes.
•Ribosomes are
• …..complex of RNA & Proteins.
• ... site of cellular protein synthesis.
• …..spheroid shape - 17 to 23 nm in dia.
• composed of 2 subunits, small subunit and a large subunit, which are produced in the
nucleolus and exported to the cytoplasm where they are assembled into a ribosome.
•Ribosomes are found in 3 different places in cells...
• 1.free in cytoplasm,plastids and mitochondria as individual subumits or dimer;
2. membrane bound on outer surface of Endoplasmic Reticulum membranes;
3. attached to mRNA molecule in a POLYSOME [or polyribosome].
Ribosomes:
(a) TEM showing ribosomes.
(b) Diagram of ribosome.
•Ribosomes are attached to mRNA molecule in a POLYSOME (or polyribosome).
The model of a text book graphic of ribosomes.
•Current Models of Ribosome Structure - crystallographic images
featured on the cover of Science magazine (Sept. 24, 1999). TWO VIEWS OF THE
STRUCTURE OF THE THERMUS THERMOPHILUS 70S RIBOSOME. TRANSFER
RNAS (GREEN, BLUE, AND YELLOW) OCCUPY A CAVITY BETWEEN TWO
RIBOSOMAL SUBUNITS.
ENDOPLASMIC RETICULUM
•is found in all eukaryotic cells with a nucleus.
•has structural continuity with the nucleus (i.e., it's contiguous).
• makes up 50% of all membranes of a cell.
• composed of flattened sheets, sacs, & tubes of membranes:
• convoluted 3-D membrane network enclosing internal spaces.
• LUMEN - internal compartment called cisternae space [up to 10% of cell's volume].
2 Types:
•Rough E.R. (with ribosomes)is typically cisternal &
•Smooth E.R. (without ribosomes) is generally tubular
•Functions:
RER: makes, transports, &
packages proteins into membrane vesicles.
SER: lipid biosynthesis and drug detoxification .
16
•Glycosylation - adding carbohydrate groups to ER proteins will help transport them to
specific cell sites.
•The endoplasmic reticulum. Rough endoplasmic reticulum is on the left, smooth
endoplasmic reticulum is on the right
•Rough Endoplasmic Reticulum with Ribosomes (TEM x61,560).
•The two pictures show that Endoplasmic Reticulum has structural continuity with
the nucleus (i.e., it's contiguous) and makes up 50% of all membranes of a cell.
• The left picture shows ER is composed of flattened sheets, sacs, & tubes of
membranes.
• The right picture shows LUMEN- internal compartment called cisternae space.
• Blobel´s research has substantially increased our understanding of the molecular
mechanisms governing these processes. Furthermore, knowledge about the signals
has increased our understanding of many medically important mechanisms. For
example, our immune system uses the signals, e.g. in the production of antibodies.
Golgi Complex and Dictyosomes
•Golgi body: In eukaryotes , a group of flat, disk-shaped sacs that are often branched into
tubules at their margins; serve as collecting and packaging centers for the cell and
concerned with secretory activities; also called dictyosomes.
•The term “Golgi complex” is used to refer collectively to all the Golgi bodies, or
dictyosomes, of a given cell.
•Golgi Complex are cell's internal membrane system for
1. endocytosis - packaging of extracellular molecules for internal digestion.
2. exocytosis (secretion) - packaging & delivery of newly synthesiszed
glycoproteins/polysaccharides for extra-cellular secretion .
•There are up to 100 Golgi bodies per cell(left)
•Golgi Apparatus in a plant parenchyma cell from Sauromatum guttatum (TEM
x145,700). Note the numerous vesicles near the Golgi.
•Structure of the Golgi apparatus and its functioning in vesicle-mediated transport.
The Endomembrane System in Eukaryotic Cells
•All eukaryotic cells have within them a functionally interrelated membrane system, the
endomembrane system consisting of the nuclear envelope, ER and Golgi apparatus, and
the plasma membrane., vesicles and other organelles derived from them.Many materials
are moved around the cell by the endomembrane system, including some proteins, and
the plasma membrane.
Cytoskeleton
17
•A network of protein fibers running throughout the cytoplasm that give a cell its shape &
provide a basis for movement (cytoplasmic streaming), which are universal in eukaryotic
cells and include
• 1. Microtubules
• 2. Microfilaments
• 3. Intermediate filaments
•Microtubules and microfilaments: either singly or collectively are responsible for nearly
all movements in eukaryotic cells.
•Intermediate filaments: ropelike cytoskeletal elements that impart mechanical strength to
cells and tissues.
The Structure and Function of Cytoskeleton
The pictures of stained cytoskeleton, TEM, SEM.
•Microtubules can be seen in a bundle in this negatively stained preparation to the left.
Then heavy metal stain is deposited around the structures, delineating their structure.
•This transmission electron micrograph to the right shows the microtubules in
longitudinal ultrathin section. Note, the tubulin molecules cannot be visualized in this
preparation.
•Collections of microtubules at the periphery of cells. They may be involved in both
motility and cytoskeletal functions in this region. It is difficult to see the structure of
separate microtubules. Microfilaments may also be accumulating in this region.
•The extensive distribution of microtubules can really be appreciated in the light
microscope after immunolabeling for tubulin with fluorescein-labeled antibodies. This
micrograph shows cells in culture labeled for tubulin. The labeling is so fine, the small
microtubules can be delineated.
Flagella and Cilia
•Flagella and Cilia are hairlike structure that extend from the surface of many different
types of eukaryotic cells.
•Cilia and flagella have the same internal structure. The major difference is in their length.
•They are thin ,about 0.2 micrometer in diameter, and vary in length from about 2 to 150
micrometers.
•They are found in some algae, other protists and plant gametes and motile sperm.
•Cilia and flagella are similar except for length, cilia being much shorter. They both have
the characteristic 9 + 2 arrangement of microtubules, the left picture shows 9+2
arrangement of microtubules in a flagellum or cilium.
•Cilia(right) from an epithelial cell in cross section (TEM x199,500). Note the 9 + 2
arrangement of cilia.
• Movement of cilia and flagella
•Flagella work as whips pulling (as in Chlamydomonas ) or pushing (dinoflagellates) the
organism through the water. Cilia work like oars (Paramecium has 17,000 such oars
covering its outer surface).
•The structure of a flagellum. (a) Diagram of a flagellum with its underlying basal body.
18
•Basal Body:
a centriole found at the base of flagella or cilia .
Cell wall
Functions of cell walls:
•Provide tensile strength and limited plasticity which are important for keeping cells from
rupturing from turgor pressure.
•Largely determines the size and shape of the cell, the texture of the tissue, and the final
form of the plant organ.
•Thick walled cells provide mechanical support.
•Tubes for long-distance transport.
•Cutinized walls prevent water loss.
•Provide protection from insects & pathogens through the production of phytoalexins or
through the synthesis and deposition of substances such as lignin.
•Physiological & biochemical activities in the wall contribute to cell-cell communication
•Contain a variety of enzymes and play important roles in the absorption, transport, and
secretion of substances in plants.
Cellulose is the principal component of plant cell wall
•Cellulose: polymer of glucose - typically consisting of 1,000 to 10,000 beta-D-glucose
residues - major component of primary and secondary wall layers.
•Cellulose molecules are united into microfibrils about 10 to 25 nanometers in diameter,
and the microfibrils wind together to form macrofibril which measures about 0.5
micrometer in diameter.
•Primary walls. Schematic diagram showing how the cellulose microfibrils are crosslinked into a complex network by hemicellulose molecules. The hemicellulose molecules
are linked to the surface of the microfibrils by hydrogen bonds. The cellulosehemicellulose network is permeated by a network of pectins, which are highly
hydrophilic polysaccharides. Both hemicellulose and pectin are matrix substances. The
middle lamella is a pectin-rich layer that cements together the primary walls of adjacent
cells.
•The detailed structure of a cell wall. (a) Portion of wall showing the middle lamella,
primary wall, and three layers of secondary wall. (b) The largest fibrils, macrofibrils, can
be seen with the light microscope. (c) With the aid of an electron microscope, the
macrofibrils can be resolved into microfibrils about 10 to 25 nanometers wide. (d) Parts
of the microfibrils, the micelles, are arranged in an orderly fashion and impart crystalline
properties to the wall. (e) A fragment of a micelle shows parts of the chainlike cellulose
molecules in a lattice arrangement.
•Cellulose forms a framework interpenetrated by a matrix of noncellulosic
molecules
•Hemicellulose
A polysaccharide composed of a variety of sugars including xylose, arabinose,
mannose;
Hemicellulose molecules are often branched. Like the pectic compounds, hemicellulose
molecules are very hydrophilic. They become highly hydrated and form gels.
Hemicellulose is abundant in primary walls but is also found in secondary walls.
19
Pectin
•Plant cell wall polysaccharide, soluble in hot aqueous solutions of chelating agents or in
hot dilute acid.
•Best known for their ability to form gel.
•Characteristics of the first-formed cell wall layers.
•Intercellular substances that cements together the walls of contiguous cells in
eudicotyledons and to a lesser extent, in monocotyledons.
Glycoprotein
•Structural proteins- as well as enzymes, which are matrix components, compose about
10 percent of the dry weight of many primany walls.
•The enzymes include peroxidases, phosphatases, cellulases, and pectinases.
•Extensins. The deposition of extension might strengthen the wall.
lignin
•Complex polymer , which is hydrophobic, laid down in the walls of plant cells such as
xylem vessels and sclerenchyma.
• Imparts considerable strength to the wall, and also protects it against degradation by
microorganisms.
•It is also laid down as a defence reaction against pathogenic attack, as part of the
hypersensitive response of plants.
Cutin, suberin, and waxes
•Fatty substances commonly found in the walls of the outer, protective tissues of plant
body.
•Cutin is found in the walls of the epidemis, and suberin is found in the secondary
protective tissue, cork.
•Both cutin and suberin occur in combination with waxes and function largely to reduce
water loss from the plant.
•Epidermal surface of a cactus seed coat (Aztekium spec.). Upper picture c: Part of the
cuticle has been blow away by ultrasound after a preceding treatment with pectinases.
• Lower Picture d: A detail of the structure shown above. The even thickness of the
cuticle is clearly recognizable. It is arranged in a system of hollow folds that cover the
smooth, unstructured cell walls of the epidermal surface. The two photos elucidate the
organization of a complex cuticle.
Cell walls consist of 3 types of layer
•Middle lamella: the first layer formed during cell division. It makes up the outer wall of
the cell and is shared by adjacent cells. It is composed of pectic compounds and protein.
20
•Primary wall: formed after the middle lamella and consists of a rigid skeleton of
cellulose microfibrils embedded in a gel-like matrix composed of pectic compounds,
hemicellulose, and glycoproteins.
•Secondary wall: formed after cell enlargement is completed. The secondary wall is
extremely rigid and provides compression strength. It is made of cellulose, hemicellulose
and lignin. The secondary wall is often layered.
•The layers of secondary cell walls. Diagram showing the organization of the cellulose
microfibrils and the three layers (S1, S2, S3) of the secondary wall. The different
orientations of the three layers strengthen the secondary wall.
•Priamry pit fields and Pits.
•Plasmodesmata are cytoplasmic strands connecting the protoplast of adjacent plant
cell.
•Light micrograph of plasmodesmata in the thick primary walls of persimmon (Diospyros)
endosperm, the nutritive tissue within the seed. The plasmodesmata appear as fine lines
extending from cell to cell across the wall.
Bordered Pit of a Pine's (Pinus silvestris) Secondary Xylem
•Electron microscopic takings. Left: Cross-section. The convex central torus has a
larger extension than the opening of the bordered pit that is enclosed by the secondary
wall. The torus is kept in its position by the primary wall material. Right: Torus in top
view. The torus is located within a net of radial fibrils partly crossing each other
produced by the primary wall material. The net is permeable for water and solutes.
21
Chapter 2 The Reproduction of Cells
This Chapter will deal with the following topics:
• Cell Division in Prokaryotes
• Cell Division in Eukaryotes
• The Cell Cycle
• Interphase
• Cell Division in Plants
• Cell Division and the Reproduction of the Organism
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. How does cell division in prokaryotes differ from that in eukaryotes? How
are the two process similar?
2. What is the cell cycle , and what events occur in the G1、S、G2，M phase?
3. What is the significance of mitosis? What events occur during each of the
four mitotic phases?
4. What role does the mitotic spindle play in positioning and then separating
sister chromatids during mitosis?
5. What roles do the phragmosome, the phragmoplast, and the cell plate play
during cytokinesis?
Cell Division in Prokaryotes
•Prokaryotes are much simpler in their organization than eukaryotes.
•The usual method of prokaryote cell division is termed binary fission.
•The prokaryotic chromosome is a single DNA molecule that first replicates, then
attaches each copy to a different part of the cell membrane.
•When the cell begins to pull apart, the replicate and original chromosomes are separated.
•There are then two cells of identical genetic composition.
•One consequence of this asexual method of reproduction is that all organisms in a
colony are genetic equals.
Cell division in a bacterium
•In prokaryotic cells, most of the genetic information is in the form of a single, long,
circular molecule of DNA, which is associated with variety of proteins.
•Attachment of the chromosome to an inward fold of the plasma membrane ensure that
one duplicated chromosome is distributed to each daughter cell as the plasma membrane
elongates.
•Rod-Shaped Bacterium, Escherichia coli, dividing by binary fission (TEM x92,750).
Cell Division in Eukaryotes
•Mitosis
22
•The division of the cell's nucleus and nuclear material of a cell;
•Consists of four stages: prophase, metaphase, anaphase, and telophase;
•Mitosis occurs only in eukaryotes;
•The DNA of the cell is replicated during interphase of the cell cycle and then segregated
during the four phases of mitosis.
•G0 Phase.
• Initials may pause in their progress around the cell cycle in response to environmental
factors, this specilized resting, or dormant state is called the G0 Phase.
The cell cycle
•Cell division, which consists of mitosis (the division of the nucleus) and cytokinesis (the
division of the cytoplasm), takes place after the completion of the three preparatory
phases (G1, S, and G2) of interphase.
Interphase
•Replication of DNA and synthesis of the proteins associated with DNA in the
chromosomes;
•Supply of organelles and other cytoplasmic components adequate for two daughter
cells,and assemble the structures needed to carry out mitosis and cytokinesis;
•This process include G1,S,and G2 phase.
S phase
•The key process of DNA replication during the cell cycle;
•A period in which many of the DNA-associated proteins, such as histones, are
synthesized.
G1 phase
•The phase which precedes the S phase, is a period of intense biochemical activity;
•The cell doubles in size and synthesizes more enzymes, ribosomes, organelles,
membrane systems, and other cytoplasmic molecules and structures;
•Some of the structures are synthesized entirely de novo within the cell like microtubules,
actin filament;
•Membranous structures is renewed and enlarged by the synthesis of lipid and protein
molecules.
G2 phase
•The phase that follows the S phase and precedes mitosis, the final preparations for cell
division;
•The cell begins to assemble the structures for allocating a complete set of chromosomes
to each daughter nucleus and for dividing the cytoplasm and separating the daughter
nuclei;
•In centriole-containing cells, duplication of the centriole pair is completed;
•By the end of the phase, the newly duplicated chromosomes begin to condense but are
difficult to distinguish from the nucleoplasm.
23
Cell Division in Plants
Diagrammatic representation of some stages of cell division in a highly vacuolate cell. (a)
Initially, the nucleus lies along one wall of the cell, which contains a large central
vacuole. (b) Strands of cytoplasm penetrate the vacuole, providing a pathway for the
nucleus to migrate to the center of the cell. (c) The nucleus has reached the center of the
cell and is suspended there by numerous cytoplasmic strands. Some of the strands have
begun to merge to form the phragmosome through which cell division will take place. (d)
The phragmosome, which forms a layer that bisects the cell, is fully formed. (e) When
mitosis is completed, the cell will divide in the plane occupied by the phragmosome.
•Phragmosome: The layer of cytoplasm that forms across the cell where the nucleus
becomes located and divides.
•Phragmoplast: A spindle-shaped system of fibrils, which arises between two daughter
nuclei at telophase and within which the cell plate is formed during cell division, or
cytokinesis. The fibrils of the phragmoplast are composed of microtubules. Phragmoplast
are found in all green algae except the members of the class Chlorophyceae and in plants.
Mitosis, a diagrammatic representation
(a) During early prophase, the chromosomes become visible as long threads scattered
throughout the nucleus. (b) As prophase continues, the chromosomes shorten and thicken
until each can be seen to consist of two threads (chromatids) attached to each other at
their centromeres. (c) By late prophase kinetochores develop on both sides of each
chromosome at the centromere. Finally, the nucleolus and nuclear envelope disappear.
d) Metaphase begins with the appearance of the spindle in the area formerly occupied by
the nucleus. During metaphase, the chromosomes migrate to the equatorial plane of the
spindle. At full metaphase (shown here) the centromeres of the chromosomes lie on that
plane. (e) Anaphase begins as the centromeres of the sister chromatids separate. The
sister chromatids, now called daughter chromosomes, then move to opposite poles of the
spindle. (f) Telophase begins when the daughter chromosomes have completed their
migration.

Photomicrograph of dividing cells in an onion(Allium sp.) root tip.
Structure of a eukaryotic chromosome
•The condensed replicated chromosomes have several points of interest;
• The kinetochore is the point where microtubules of the spindle apparatus attach;
•Replicated chromosomes consist of two molecules of DNA (along with their associated
histone proteins) known as chromatids;
•The area where both chromatids are in contact with each other is known as the
centromere.
24



A diagram of a fully condensed chromosome. The chromosomal DNA was replicated
during the S phase of the cell cycle. Each chromosome now consists of two identical
parts, called sister chromatids. The centromere, the constricted area in the center, is
the site of attachment of the two chromatids. The kinetochores are protein-containing
structures, one on each chromatid, associated with the centromere. Attached to the
kinetochores are microtubules that form part of the spindle.
Mitotic spindle at metaphase, consisting of kinetochore microtubules and overlapping
polar microtubules. Note that the minus ends of the microtubules are at or near the
poles and the plus ends away from the poles. Following a tug-of-war, the
chromosomes have come to lie on the equatorial plane.
In plant cells, separation of the daughter chromosomes is followed by formation of a
cell plate, which complete the separation of the dividing cells. Here numerous Golgi
vesicles can be seen fusing in an early stage of cell plate formation.The two groups of
chromosomes on either side of the developing cell plate are at telophase. Arrows
point to portions of the nuclear envelope reorganizing around the chromosomes.
Duration of mitosis
•Varies with the tissues and the organism involved.
•Prophase is always the longest phase and anaphase is always the shortest.
•In root tip, the relative lengths of time for each of the four phases are as follows:
Prophase: 1 to 2 hours;
Metaphase: 5 to 15 minutes;
Anaphase: 2 to 10 minutes;
Telophase:10 to 30 minutes;
•Duration of Interphase: 12 to 30 hours.
Structure and main features of a spindle apparatus
•During mitosis replicated chromosomes are positioned near the middle of the cytoplasm
and then segregated so that each daughter cell receives a copy of the original DNA;
•Plants and most other eukaryotic organisms lack centrioles;
•Prokaryotes, of course, lack spindles and centrioles.
Cytokinesis
•
•
•
The process of splitting the daughter cells apart ;
The splitting of the cytoplasm and allocation of the golgi, plastids and cytoplasm
into each new cell.
Cytokinesis in plants occurs by the formation of a phragmoplast and a cell plate.
Cell division and the reproduction of the organisms
•In many one-celled organisms, mitosis is the key event in reproduction.
•Mitosis plays the same essential role in the reproduction of some large organismsAsexual reproduction( vegetative reproduction).
25
•Sexual reproduction-the fusion of two cells, the sperm and egg.
26
Chapter 3 Meiosis and Sexual Reproduction
In this chapter we’ll deal with the following topics:
•
•
•
•
•
•
•
Haploid and Diploid
Meiosis, the Life Cycle, and Diploidy
The Process of Meiosis
The Phases of Meiosis
Asexual Reproduction: An Alternative Strategy
Advantages of Sexual Reproduction
Comparison of the Main Features of Mitosis and Meiosis
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What is the relationship between haploid and diploid chromosome numbers
and meiosis and fertilization ?
2. What is the principal difference between zygotic meiosis, gametic meiosis,
and sporic meiosis?
3. How is a sporophyte different from a gametophyte, and what is meant by the
term “alternation of generations”?
4. What are the events that occur during crossing-over, and why is this process
so important?
5. What are the main events that occur during meiosis Ι? How is meiosis Ι
different from meiosis Ⅱ?
6. What are the advantages and disadvantages of sexual and asexual
reproduction?
Haploid and Diploid
•Sexual reproduction is characterized by two events:
•The halving of the number of chromosomes (meiosis) and the coming together of the
gametes (fertilization).
•Following meiosis, there is a single set of chromosomes--that is, the haploid number (n);
here n = 2.
•Following fertilization, there is a double set of chromosomes--that is, the diploid number
(2n).
•Haploid Cells that contain only one member of each homologous pair of
chromosomes (haploid number = n). At fertilization, two haploid gametes fuse to
form a single cell with a diploid number of chromosomes.
27
•Diploid Cells that contain homologous chromosomes. The number of chromosomes
in the cells is the diploid number and is equal to 2n (n is the number of homologous
pairs).
Homologous chromosomes.
•(a) During or prior to gamete formation, individual homologs (members of a
homologous pair) are parceled out by meiosis so that a haploid (n) gamete carries only
one member of each homologous pair.
•(b) At fertilization, the chromosomes in the sperm nucleus and the egg nucleus come
together in the diploid (2n) zygote, producing once again pairs of chromosomes.
•Each pair consists of one homolog from one parent (paternal chromosome) and one from
the other parent (maternal chromosome).
•Homologous chromosomes: Chromosomes that associate in pairs in the first stage of
meiosis; each member of the pair is derived from a different parent.
•Homologous chromosomes are also called homologs.
Meiosis, the Life Cycle, and Diploidy
Diagrams of the principal types of life cycles. In these diagrams, the diploid phase of the
cycle takes place below the broad bar, and the haploid phase occurs above it.
a) In zygotic meiosis, the zygote divides by meiosis to form four haploid cells;
•Each of these cells divides by mitosis to produce either more haploid cells or a
multicellular haploid individual that eventually gives rise to gametes by differentiation;
•This type of life cycle is found in Chlamydomonas and a number of other algae and in
the fungi.
b) In gametic meiosis, the haploid gametes are formed by meiosis in a diploid individual
and fuse to form a diploid zygote that divides to produce another diploid individual;
•This type of life cycle is characteristic of most animals and some protists (Oomycota,
the water molds), as well as some green and brown algae (for example, Fucus, a brown
alga).
•(c) In sporic meiosis, the sporophyte, or diploid individual, produces haploid spores as a
result of meiosis. These spores do not function as gametes but undergo mitotic division;
•This gives rise to multicellular haploid individuals (gametophytes), which eventually
produce gametes that fuse to form diploid zygotes;
•These zygotes, in turn, differentiate into diploid individuals. This kind of life cycle,
known as alternation of generations, is characteristic of plants and many algae.
Some terms associated with meiosis
•alternation of generations:
28
A life cycle in which a multicellular diploid stage is followed by a haploid stage and so
on; found in land plants and many algae and fungi.
 alternation of isomorphic generations:
the haploid and diploid forms, or generations are similar in external appearance.
 Alternation of heteromorphic generations
the haploid and diploid forms are not identical, in this way, the gametophyte and
sporophyte became noticeably different from one another.
 gametes
Haploid reproductive cells (ovum and sperm).
 gametophyte
The haploid stage of a plant exhibiting alternation of generations, generates gametes by
the process of mitosis.
 sporophyte
The diploid stage of a plant exhibiting alternation of generations. The diploid, spore
producing phase of the plant life cycle.


Life cycle of a fern, illustrating the alternation of generations that characterizes plants.
The sporophyte and gametophyte of Lily.
The process of Meiosis
•(a) A homologous pair of chromosomes, prior to meiosis. One member of the pair is of
paternal origin, and the other of maternal origin.
•Each of these chromosomes has duplicated and consists of two sister chromatids
connected at the centromere.
•(b) In prophase of the first meiotic division, the two homologs come together and
become closely associated with one another.
•The paired homologous chromosomes are called a bivalent.
•A homologous pair consists of four chromatids and is therefore also known as a tetrad.
•Within the tetrad, chromatids of the two homologs intersect at a number of points,
making possible the exchange of chromatid segments.
•This phenomenon is known as crossing-over, and the locations at which it occurs are
called chiasmata.
•So, crossing-over can be defined as the exchange of corresponding segments of genetic
material between the chromatids of homologous chromosomes at meiosis.
•c) The result of crossing-over is a recombination of the genetic material of the two
homologs.
•The sister chromatids of each homolog are no longer identical.
•Kinetochore microtubules attached to the fused kinetochores of sister chromatids
separate the homologs at anaphase I.
The Phases of Meiosis
•Meiosis consists of two successive nuclear divisions,which are designated as meiosis І
(reduction) and meiosis II(division).
•In meiosis І, homologus chromosomes pair and then separate from one another.
•In meiosis II , the chromatids of each homolog separate.
•The cells in which meiosis occurs are called meiocytes.
29
Prophase I
•Prophase I is one of the most important stages of meiosis.
The chromotid threads begin to twist and condense, creating chromosomal structures
which are visible to the microscope.
•Each chromosome then actively seeks out its homologous chromosome, as shown in the
graphical representation.
•After the homologous chromosomes pair, the structure is referred to as a tetrad (four
chromatids)
•The point at which two non-sister chromatids intertwine is known as a chiasma.
•Sometimes a process known as crossing over occurs at this point. This is where two
non-sister chromatids exchange genetic material.
•This exchange does not become evident, however, until the two homologous pairs
separate.
Five Substages of Prophase I
•Leptotene
•During this stage, the chromosomes begin to condense and become visible. Researchers
also believe that homologous pair searching begins also at this stage .
•Zygonema
The chromosomes continue to become denser. The homologous pairs have also found
each other and begin to initially align with one another, referred to as synapsis. Lateral
elements also form between the two homologous pairs, forming a synaptonemal complex.
•Portion of a typical synaptonemal complex, which appears to be essential for crossingover. Recombination nodules are protein complexes that appear to mediate the process.
•Pachynema
Coiling and shortening continues as the chromosomes become more condense. A
synapsis forms between the pairs, forming a tetrad.
•Diplonema
The sister chromatids begin to separate slightly, revealing points of the chiasma. This is
where genetic exchange occurs between two non-sister chromatids, a process known as
crossing over.
•Diakinesis
The chromosomes continue to pull apart, but non-sister chromatids are still loosely
associated via the chiasma.
•The chiasma begin to move toward the ends of the tetrad as separation continues.
•This process is known as termianilization.
•Also during diakinesis, the nuclear envelope breaks down and the spindle fibers begin to
interact with the tetrad.
•Prophase I has a unique event -- the pairing (by an as yet undiscovered mechanism) of
homologous chromosomes.
•Synapsis is the pairing of homologous chromosomes that occurs prior to the first
meiotic division; crossing-over occurs during synapsis.
30
•The resulting chromosome is termed a tetrad, being composed of two chromatids from
each chromosome, forming a thick (4-strand) structure.
•Crossing-over may occur at this point. During crossing-over chromatids break and may
be reattached to a different homologous chromosome.
•Slide showing Crossing-over between homologous chromosomes produces
chromosomes with new associations of genes.
Comparison of Mitosis and Meiosis
•Two nuclear divisions are involved in meiosis and only one in mitosis, yet in both
meiosis and mitosis the DNA is replicated only once.
•Each of the four nuclei produced in meiosis is haploid- containing only one-half the
number of chromosomes-that is, only one member of each pair of homologous
chromosomes-present in the original diploid nucleus from which it was produced. By
contrast, each of the two nuclei produced during mitosis has the same number of
chromosomes as the original nucleus.
•Each of the nuclei produced by meiosis contains different gene combinations from the
others, whereas the nuclei produced by mitosis have identical gene combination.
•Summary: Comparison of the Features of Mitosis and Meiosis.
31
Chapter 4 Cells and Tissues of the Plant Body
In this chapter we’ll study the following topics:
•Apical Meristems and Their Derivatives
•Growth, Morphogenesis, and Differentiation
•Internal Organization of the Plant Body
•Dermal Tissues
•Ground Tissues
•Vascular Tissues
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What is the role of the apical meristems, and what is their composition?
2. What are the three overlapping processes of plant development, and how do
they overlap?
3. What are the three tissue systems of the plant body? Of what tissues are they
composed?
4. How do parenchyma, collenchyma, and sclerenchyma cells differ from one
another? What are their respective function?
5. What are the principal conducting cells in the xylem? In the phloem? What
are the characteristic features of each cell type?
6. What roles are played by epidermis?
Apical Meristems and Their Derivatives



Apical meristems are found at the tips of all roots and stems and are involved
primarily with extension of the plant body.
The term “Apical Meristem” refer to a population of cells composed of initials
and their immediate derivative.
Initials are the cells that divide in such a way that one the sister cells remains in
the meristem as an initial while the other becomes a new body cell or derivative.
Shoot and root apical meristems
•Longitudinal section of a shoot tip of lilac (Syringa vulgaris,丁香),showing the shoot
apical meristem and primordia of leaves and axillary buds.
• Root tip of radish (Raphanus sativus), in longitudinal section, showing the root apical
meristem covered by a rootcap. Protoderm, procambium, and ground meristem are partly
differentiated tissues known as primary meristems.
Primary meristem
32
•Primary meristem-protoderm, procambium, and ground meristem-are initiated during
embryogenesis
and are extended throughout the plant body by the activity of the apical meristem;
•These primary meristems are partly differentiated tissues that remain meristematic for
some time before they begin to differentiate into specific cell types in the primary tissues;
•Growth of this type, which involves extension of the plant body and formation of the
primary tissues, is called primary growth.
Diagram summarizing the origin, from the apical meristem, of the primary
meristems, which give rise to the tissue systems and tissues of the primary plant
body.
Growth, Morphogenesis, and Differentiation
•Growth can be defined as an irreversible increase in size, which is accomplished by a
combination of cell division and cell enlargement.
•Cell division simply increase cell number without increasing the overall volume of a
structure.
•Most plant growth is brought about by cell enlargement.
•Morphogenesis
The acquisition of a particular shape or form.
•Differentiation
The process by which cells that have identical genetic constitutions become different
from one another and from the meristematic cells from which they originated-often
begins while the cell is still enlarging.
Diagram illustrating some of the cell types that may originate from a meristematic
cell of the procambium or the vascular cambium.
Internal Organization of the Plant Body
Plant tissue and system
1. Cells that work together to perform a specific function form a Tissue.
2. Tissues are arranged into Systems in Plants, including the Dermal Tissue System,
Ground Tissue System, and Vascular Tissue System.
3. These Systems are further organized into the three Major Plant Organs - THE ROOTS,
STEMS AND LEAVES.
Characteristics of Plant Tissue Systems
DERMAL TISSUE SYSTEM
1. DERMAL TISSUE forms the SKIN (the outside covering) of a Plant, Covering all
parts of the ROOTS, STEMS, AND LEAVES.
2. One kind of Dermal tissue is the EPIDERMIS, made of Parenchyma Cells, which is
usually only one cell thick, and is the outer protective tissue of young plants and mature
non-woody Plants.
33
3. Dermal Tissue has different functions, depending on its LOCATION on the plant
4. Above the ground, Dermal Tissue prevents the plant from drying out by reducing
water loss from evaporation (Transpiration). This Dermis Tissue also Secrets a Waxy
Layer called CUTICLE.
5. Below the ground, Dermal Tissue absorbs Water. On the underground parts of a plant,
the Epidermis forms ROOT HAIRS that absorb water and nutrients.
6. On leave and stem openings in the epidermis are called Stomata. Stomata regulate the
passage of gases and moisture into and out of the plant.
7. In woody stems and roots, the Epidermis is replaced by Dead Cork Cells.
8. Periderm is Secondary Protective Tissue, which replaces the epidermis in stems and
roots having secondary growth.
Electron micrographs of maize (Zea mays) stomata.
(a) Section taken parallel to the surface of the leaf showing open pore between
immature guard cells, whose walls have not yet thickened, and two associated subsidiary
cells.
(b) Transverse section through closed stoma. Each thick-walled guard cell is attached
to a subsidiary cell. The interior of the leaf is below.
Diagram of a mature stoma, showing its relationship to the epidermis and
underlying cells. The walls next to the pores of stomata are generally thicker than those
adjacent to other epidermal cells. While the stomata are being formed, they may be raised
above or recessed below the surface of the epidermis. Often there is a large air space, or
substomatal chamber, just behind the stoma. Unlike other epidermal cells, guard cells
contain chloroplasts.
Cuticle of Clivia sp.（君子兰）(left) - The cuticle forms an impervious boundary
between the cells in the leaf and the environment. The cuticle keeps pathogens out. It also
keeps water inside the leaf. Plants that grow in extremely dry (Xeric) environments
usually have a thick cuticle. Lignification of the cell walls may also occur.
The Cuticle from both sides of Coconut Palm leaves(right) is very thick and stains
positively with Sudan Red IV.
•SEM images of Cannabis（大麻） trichomes(left). Note the variety! Some are
sessile while others are stalked
Arabadopsis leaf Trichomes(middle) seen from above with crossed Polarizers .
Arabadopsis leaf Trichomes(right) seen from the side with crossed Polarizers.
•Transverse section of the periderm from the stem of apple (Malus sylvestris). The
periderm shown here consists largely of cork cells, which are laid down to the outside
(above) in radial rows by the cells of the cork cambium. One or two layers of phelloderm
cells lie below the cork cambium.
•GROUND TISSUE SYSTEM
1. Ground Tissue System is surrounded by Dermal Tissue, which consists of three types
of Plant tissues- Parenchyma tissue, Collenchyma Tissue, and Sclerenchyma Tissue.
34
2. Ground Tissue consists of everything that is not Dermal Tissue or Vascular
Tissue. Parenchyma, a simple tissue, makes up most Ground Tissue.
3. Ground Tissue has many metabolic functions, including PHOTOSYNTHESIS, FOOD
STORAGE, SECRETION, AND SUPPORT.
4. Non-woody roots, stems, and leaves are made up primarily of Ground Tissue.
5. Ground Tissue System consists of Parenchyma cells, Collenchyma cells, and
Sclerenchyma cells.
•PARENCHYMA CELLS
1. The most Abundant and Least Structurally Specialized Cells.
2. Parenchyma Cells are usually loosely packed cubed-shaped or elongated cells that
contain a large central vacuole and have thin, flexible cell walls.
3. Cells occur throughout the plant and have many functions, INCLUDING
PHOTOSYNTHESIS, FOOD STORAGE,SECRETION, AND GENERAL
METABOLISM (photosynthesis, storage of water and nutrients, and healing).
4. AN IMPORTANT CHARACTERISTICS OF PARENCHYMA CELLS IS THAT
THEY CAN DIVIDE AND BECOME SPECIALIZED FOR VARIOUS FUNCTION.
5. These cells usually form the bulk of non-woody plants. For example, the fleshy part
of an apple is made mostly of parenchyma cell.
Picture a. Parenchyma cells (below) and collenchyma cells with unevenly thickened walls
(above), seen in a transverse section of the cortex of an elderberry (Sambucus canadensis)
stem.b. Diagram of a series of parenchyma cells(middle).c. Lily Parenchyma Cell (crosssection) (TEM x7,210)(right).Note the large nucleus and nucleolus in the center of the
cell, mitochondria and plastids in the cytoplasm.
•Transfer Cells Are Parenchyma Cells with Wall Ingrowths
Transverse section of a portion of the phloem from a small vein of a Sonchus (sow
thistle，苦苣菜) leaf, showing transfer cells with their numerous wall ingrowths.
•COLLENCHYMA CELLS:
1. Collenchyma cells, like parenchyma cells, are living at maturity.
2. The cell walls of Collenchyma Cells are thicker than those of Parenchyma
Cells. Collenchyma cell walls are also irregular in shape. The thicker cell walls provide
more support for the plant.
3.The most distinctive feature is their unevenly thickened, nonlignified primary walls,
which are soft and pliable and have a glistening appearance in fresh tissue.
4. Collenchyma cells are usually grouped in Strands. They are specialized for supporting
regions of the plant that are still lengthening. The tough string of a Celery Stalk (Stems)
are made of Collenchyma Cells.
35
•Transverse section of collenchyma tissue from a petiole in rhubarb (Rheum
rhabarbarum，大黄)(left). In fresh tissue like this, the unevenly thickened collenchyma
cell walls have a glistening appearance.
Collenchyma cells(right) are distinguished from parenchyma cells by irregular secondary
wall thickening of cellulosic material in the cell corners. Parenchyma cells have no
secondary thickening.
•SCLERENCHYMA CELLS
1. Support the NON-Growing Parts of plants.
2. Sclerenchyma cells have thick, even rigid , and lignified secondary walls. They
support and strengthen the plant in areas where growth is No Longer Occurring.
3. They have thick, NONSTRECHABLE cell walls.
4. The cell walls are so thick that the cell usually dies at maturity, providing a frame to
support the plant.
5. When they mature, most sclerenchyma cells are empty chambers surrounded by thick
walls.
6. There are two types of Sclerenchyma cells : fibers and sclereids.
Two types of Sclerenchyma cells
A. FIBERS - cells up to 70 mm long that usually occur in strands. FABRIC such as
linen and flax are made of these fibers.
B. SCLEREIDS - have thicker cell walls than fibers, have many shapes, and can occur
singly or in small groups. The gritty texture of a pear is from Sclereids it
contains. Sclereids also cause the hardness of a peach pit and a walnut shell.
•Primary phloem fibers from the stem of a linden, or basswood (Tilia americana), seen
here in both (a) cross-sectional and (b) longitudinal views. The secondary walls of these
long, thick-walled fibers contain relatively inconspicuous pits. Only a portion of the
length of these fibers can be seen in (b).
•Branched sclereid from a leaf of the water lily (Nymphaea odorata), a magnoliid, as
seen in (a) ordinary light and (b) polarized light. Numerous small, angular crystals of
calcium oxalate are embedded in the wall of this sclereid.
•Sclereids (stone cells) from fresh tissue of the pear (Pyrus communis) fruit. The
secondary walls contain conspicuous simple pits with many branches, known as
ramiform pits. During formation of the clusters of stone cells in the flesh of the pear fruit,
cell divisions occur around some of the sclereids formed earlier. The newly formed cells
differentiate as stone cells, adding to the cluster.
VASCULAR TISSUE SYSTEM
•Vascular plants have specialized Tissue called Vascular Tissue. Vascular Tissue carries
water and nutrients throughout the plant and helps support the plant.
36
2. There are two kinds of Vascular Tissue; both Kinds of Vascular Tissue contain
specialized conducting cells:
A. XYLEM - moves water and minerals upward from roots to leaves.
1) When Water and Minerals are absorbed by the Roots of a Plant, These substances must
be transported up to the Plant's Stems and Leaves.
2) XYLEM is the tissue that carries water and dissolved substance upward in the plant.
3) Two kinds of conducting cells are present in Xylem of ANGIOSPERMS:
TRACHEIDS and VESSEL ELEMENTS. Both types of cells do not conduct Water until
they are dead and empty.
4) TRACHEIDS are long, thick walled sclerenchyma, narrow cells of xylem with thin
separation between them. Water moves from one TRACHEID to another through PITS,
which are thin, porous areas of the cell wall.
5) VESSEL ELEMENTS are short, SCLERENCHYMA, wide cells of XYLEM with no
end walls. Vessel Elements DO NOT have separations between them; they are arranged
end to end liked barrels stack on top of each other. These Vessels are wider than
Tracheids, and more water moves through them.
6) Angiosperms, or Flowering Plants, contain Tracheids and Vessel Elements.
7) Seedless vascular plants, Gymnosperms, or cone bearing seed plants, contain Only
Tracheids.
Two Kinds of Conducting Cells in Xylem of ANGIOSPERMS: TRACHEIDS and
VESSEL ELEMENTS.
B. PHLOEM moves sugars or saps in both direction throughout the plant originating in
the leaves.
1) Sugars made in the leaves of a plant by
photosynthesis must be transported throughout the plant.
2) Phloem Tissue conducts sugars upward and downward in a plant.
3) The sugars move as Sugary Sap.
37
4) TWO Kinds of Cells are present in Phloem: SIEVE TUBE MEMBER AND
COMPANION CELLS.
5) SIEVE TUBES MEMBERS ARE CELLS OF PHLOEM THAT CONDUCT SAP.
Sieve Tube members are stacked to form long SIEVE TUBES. Compounds move from
Cell to Cell through End Walls called SIEVE PLATES.
6) COMPANION CELLS are parenchyma cells of phloem that enable the sieve tube
elements to function.
7) Each Sieve Tube Element has a Companion Cell. Companion cells control the
movement of substances through the sieve tubes.
8) The partnership between these two cells is vital; Neither Cell can Live without the
other.
•Conducting Cells in Xylem and Phloem
•Transverse section of a vascular bundle from the stem of a squash (Cucurbita maxima),
a favorite species for the study of phloem.
Phloem occurs both exterior to and interior to the xylem in squash vascular bundles.
Typically, a vascular cambium develops between the external phloem and the xylem but
not between the internal phloem and the xylem.
•Cell types in the secondary xylem, or wood, of an oak tree (Quercus). (a), (b) Wide
vessel elements, and (c) a narrow vessel element. (d) Tracheid. (e), (f) Fibers.
•The spotted appearance of these cells is due to pits in the walls; pits are not discernible
in (f). Pits are areas lacking secondary walls.
•Only the vessel elements have perforations, which are areas lacking both primary and
secondary cell walls.
•Parts of tracheary elements from the first-formed primary xylem (protoxylem) of the
castor bean (Ricinus communis). (b) Double helical thickenings in elements that have
been extended. The element on the left has been greatly extended, and the coils of the
helices have been pulled far apart.
•Diagram illustrating development of a vessel element. (a) Young, highly vacuolated
vessel element without a secondary wall. (b) The cell has expanded laterally, secondary
wall deposition--in the form of a helix (c) Secondary wall deposition has been completed.
The nucleus is degenerating, the tonoplast is ruptured, and the wall at the perforation site
has partly disintegrated. (d) The cell is now mature; it lacks a protoplast and is open at
both ends.
•Sieve cells. (a) Longitudinal (radial) view of secondary phloem of yew (Taxus
canadensis), a conifer, showing vertically oriented sieve cells, strands of parenchyma
cells, and fibers. Parts of two horizontally oriented rays can be seen traversing the vertical
38
cells. (b) Detail of portion of the secondary phloem of yew, showing sieve areas (arrows),
with callose（胼胝质） (stained blue) on the walls of the sieve cells, and albuminous
cells, which here constitute the top row of cells in the ray.
•Sieve-tube elements. (a) Longitudinal (radial) view of secondary phloem of basswood
(Tilia americana), showing sieve-tube elements, with sieve plates, and conspicuous
groups of thick-walled fibers.(b ) Compound sieve plates of basswood sieve-tube
elements. The sieve plates of basswood, seen here in detail, are known as compound
sieve plates because they consist of two or more sieve areas. Each sieve area is composed
of pores bordered by cylinders of callose, which are stained blue in this section.
• Immature and mature sieve-tube elements in the phloem in the stem of squash
(Cucurbita maxima), as seen in photomicrographs. (a) Transverse section, showing two
immature sieve-tube elements. P-protein bodies (arrows) can be seen in the sieve-tube
element on the left, an immature sieve plate in the one to the right, above. The sieve
plates of squash are simple sieve plates (one sieve area per plate). The small, dense cells
are companion cells.
•(b) Transverse section showing two mature sieve-tube elements. A slime plug can be
seen in the sieve-tube element on the left; a mature sieve plate can be seen in the one on
the right. The small, dense cells are companion cells.
•(c) Longitudinal section showing mature and immature sieve-tube elements. The arrows
point to P-protein bodies in immature cells.
•Differentiation of a sieve-tube element. (a) The mother cell of the sieve-tube element
undergoing division. (b) Division has resulted in formation of a young sieve-tube element
and a companion cell. After division, one or more P-protein bodies arise in the cytoplasm,
which is separated from the vacuole by a tonoplast. The wall of the young sieve-tube
element has thickened, and the sites of the future sieve-plate pores are represented by
plasmodesmata. Each plasmodesma is now surrounded by a platelet of callose on either
side of the wall.
• (c) The nucleus is degenerating, the tonoplast is breaking down, and the P-protein
bodies are dispersing in the cytoplasm lining the wall. At the same time, the
plasmodesmata of the developing sieve plates are beginning to widen into pores.
•(d) At maturity, the sieve-tube element lacks a nucleus and a vacuole. All of the
remaining protoplasmic components, including the P-protein, line the walls, and the
sieve-plate pores are open. The callose platelets were removed as the pores widened. Not
shown here but also present in the mature sieve-tube element are smooth endoplasmic
reticulum, mitochondria, and plastids.
39
40
Chapter 5 The Root: Structure and Development
In this Chapter we’ll deal with the following topics:
•
•
•
•
•
•
•
Root Systems
Origin and Growth of Primary Tissues
Primary Structure
Effect of Secondary Growth on the Primary Body of the Root
Origin of Lateral Roots
Aerial Roots and Air Roots
Adaptations for Food Storage
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What are the two principal types of root systems, and how do they differ
from one another?
2. What changes occur to the rootcap during elongation of the root, and what
are some functions of the rootcap?
3. What are the two main types of apical organization, and how do they differ
from one another?
4. What tissues are found in a root at the end of primary growth, and how they
are they arranged?
5. What effect does secondary growth have on the primary body of the root?
6. Why are lateral roots said to be endogenous?
Root Systems
1. THE FIRST ROOT TO EMERGE FROM A SEED IS THE PRIMARY ROOT. As
the plant matures, branches grow from the Primary Root.
2. In some Plants the Primary Root Enlarges, If this first Root Becomes the Largest Root
it is called a TAPROOT (THE LARGEST ROOT).
3. Taproots can grow deep, reaching water far below the surface of the ground.
4. Beets and Carrots are plants with Taproots that are used for Food.
5. Not all plants have Taproots, especially Monocots, such as grasses, the Roots are
Numerous and all about the same size.
6. NUMEROUS, EXTENSIVELY BRANCHED ROOTS ARE CALLED FIBROUS
ROOTS. These roots grow near the surface and can collect water in a wide area. Because
of the numerous branches of the roots, these plants are excellent for preventing Erosion
(Grasses). Fibrous Roots of Monocots often develop from the base of the Stem rather
than from other roots.
7. A few plants have special roots called ADVENTITIOUS ROOTS. ROOTS THAT
FORM ON A STEM OR LEAF. SOME GROW ABOVE GROUND AND HAVE
SPECIAL FUNCTIONS -CORN - PROP ROOTS HELP SUPPORT THE PLANT.
41
8.Air Roots of Orchids, obtain water and mineral nutrients from the Air. Air
roots on the Stems of Ivy（常春藤） and other vines enable them to climb walls
and trees.
• TYPES OF ROOTS:
Taproot of Carrot (Left)
Fibrous Roots of Monocots (Middle)
Prop Roots of Corn
•
•
Diagrams of oat (Avena sativa) plants, showing relative sizes of the root and shoot
systems (a) 31, (b) 45, and (c) 80 days after planting. The oat plant, a monocot, has a
fibrous root system. The roots are involved primarily with anchorage and absorption.
Each of the vertical units depicted here represents 1 foot (approximately 30.5
centimeters).
Two types of root systems, as represented by two prairie plants. (a) Taproot system of
the blazing star (Liatris punctata，斑点蛇斑菊), a eudicot. (b) Fibrous root system
of wire grass (Aristida purpurea，紫三芒草), a monocot. Each of the vertical units
depicted here represents 1 foot (approximately 30.5 centimeters). Taproot systems
generally penetrate deeper into the soil than fibrous root systems.
Origin and Growth of Primary Tissues
1. The Root TIP is covered by a Protective ROOT CAP, which covers the Apical
Meristem.
2. The Root Cap produces a Slimy Substance that functions like Lubricating Oil,
allowing the root to move more easily through the soil as it grows
3. Cells that are crushed or knocked off the root Cap as the root moves through the soil
are replaced by new cells produced in the Apical Meristem, where cells are continuously
dividing.
4. Roots do not absorb water and minerals through a smooth Epidermis. Tiny, hairlike
projections called ROOT HAIRS on the epidermis absorb water and dissolved minerals
from the soil. Root Hairs also INCREASE the Surface Area of the Plant Roots.
5. The Core of a root consists of a Vascular Cylinder. The Vascular Cylinder contains
Xylem and Phloem. Surrounding the Vascular Cylinder is a band of Ground Tissue
called the CORTEX. Outside the Cortex is the EPIDERMIS.
6. The arrangement of Xylem and Phloem differs in the roots of Monocots and Dicots.
A. DICOTS - In Dicots the Vascular Tissue forms a solid core at the center of the root.
B. MONOCOTS - In Monocots the Vascular Tissue forms a ring that surrounds a
central region of Cells known as PITH.
7. The Vascular Cylinder is separated from the Cortex by a tightly packed layer of
cells. The layer of cells that separates the Cortex from the Vascular Cylinder is called the
ENDODERMIS (cell layer like a row of bricks);
8. Where the cells of the endodermis touch each other, they are coated with a waxy layer
called the CASPARIAN STRIP;
42
9. The Casparian Strip blocks the movement of Water between adjacent cells of the
Endodermis;
10. This Causes the water and dissolved minerals that enter a root to be channeled
through the cytoplasm of the cells of the Endodermis into the Vascular Tissue.
11. The outermost layer or layers of the Central Vascular Tissue is termed the
PERICYCLE. Lateral Roots are formed by the division of Pericycle Cells.
12. Dicots and Gymnosperms Roots often experience Secondary Growth. Secondary
Growth begins when the Vascular Cambium forms between Xylem and Phloem.
13. Pericycle Cells form the vascular cambium. The Vascular Cambium produces
Secondary Xylem toward the Inside of the Root and Secondary Phloem toward the
Outside.
•
A portion of a eudicot root, showing the spatial relationship between the rootcap and
region of root hairs, and (near the top) the sites of emergence of lateral roots, which
arise from deep within the parent root. New root hairs arise just behind the region of
elongation at about the same rate as the older hairs die off. The root tip is covered by
a mucigel sheath, which lubricates the root during its passage through the soil.
•Closed type of root apical organization, as seen in an apical meristem of a maize (Zea
mays) root tip, in longitudinal section. Notice the three distinct layers of initials. The
lower layer gives rise to the rootcap, the middle layer to the protoderm and to the ground
meristem, or cortex, and the upper layer to the procambium or vascular cylinder.
•
Open type of root apical organization, as seen in longitudinal sections of onion
(Allium cepa) root tip. (a) The primary meristems--protoderm, procambium, and
ground meristem--can be distinguished close to the apical meristem.
•
Open type of root apical organization, as seen in longitudinal sections of onion
(Allium cepa) root tip. (b) Detail of the apical meristem.
•
Diagram illustrating early stages in the primary development of a root tip. The region
of cell division extends for a considerable distance behind the apical meristem. These
cell divisions overlap with cell elongation and enlargement and also with cell
maturation, or differentiation. At various distances from the apical meristem, cells
enlarge and develop as specific cell types according to their position in the root.
• Primary structure of roots
•The epidermis in young roots absorbs water and minerals, the uptake of which is
facilitated by root hairs.
•Root hairs. (b) Root of a bentgrass (Agrostis tenuis,细弱剪股颖) seedling. The root hairs
may be as much as 1.3 centimeters long and may attain their full size within hours. Each
hair is comparatively short-lived, but the formation of new root hairs and the death of old
ones continue as long as the root is growing.
The structure of root
43
•Ranunculus root, transverse section(left)
•Close up of stele with endodermis(right)
•Transverse section of the root of a buttercup (Ranunculus).
(a) Overall view of mature root. (b) Detail of outer portion of a mature root.In this root,
the epidermis has died and the exodermis, the outer layer of cells of the cortex, has
replaced the epidermis as the functional surface layer. Note intercellular spaces(arrows)
among the cortical cells interior to the compactly arranged exodermis. The intercellular
spaces are essential for aeration of the root cells.
•Transverse sections of a maize (Zea mays) root. (a) Overall view of mature root. Part
of a lateral root is indicated by the arrow. The vascular cylinder, with its pith, is quite
distinct.
•Transverse sections of a maize (Zea mays) root. (b) Detail of outer portion of a mature
root, showing the epidermis with root hairs and part of the cortex. The outer layer of
cortical cells is differentiated as a compactly arranged exodermis. Note intercellular
spaces (arrows) among the other cortical cells.
•Transverse sections of a maize (Zea mays) root. (c) Detail of immature vascular
cylinder. (d) Detail of mature vascular cylinder.
•The cortex represents the ground tissue system in most roots
High-magnification view of a portion of an immature buttercup (Ranunculus) root,
showing Casparian strips in the endodermal cells. Notice that the plasmolyzed protoplasts
of the endodermal cells cling to the strips.
•Endodermis is a Cylinder of single layer of cells, just inside the cortex. The cells have
a thick waxy band, the Casparian strip. The Casparian strip regulates the flow of water
between the outer portion of the root and the inner vascular tissues.
•Transverse section of a radial anticlinal wall between two endodermal cells in the
root of field bindweed (田旋花 Convolvulus arvensis). The region of the Casparian
strip is more intensely stained than the rest of the wall. Notice how firmly the plasma
membrane adheres to the wall in the region of the Casparian strip in each of these
plasmolyzed cells.
•Electron micrograph showing a section through the cell wall between two adjacent
endodermal cells of a squash(Cucurbita pepo) root. In this late stage of differentiation
of the endodermis, suberin lamellae are covered by cellulose wall. Note the alternating
light and dense bands in the suberine lamellae, which are interpreted as consisting of wax
and suberine, respectively.
Three-dimensional diagrams showing three developmental stages of an endodermal
cell in a root that remains in a primary state. (a) Initially, the endodermal cell is
characterized by the presence of a Casparian strip in its anticlinal walls. (b) Then a
suberin lamella is deposited internally over all wall surfaces. c) Finally, the suberin
44
lamella is covered internally by a thick, often lignified, layer of cellulose. The outside of
the root is to the left in all three diagrams.
The vascular cylinder includes the primary vascular tissues and pericycle
•Dicot roots typically have vascular cylinders arranged with xylem in the middle in an X,
and phloem in between the arms - monocot roots have vascular cylinders with xylem and
phloem arranged in bundles outside of the pith.
Effect of Secondary Growth on the Primary Body of the Root
•Secondary growth in roots consists of the formation of secondary vascular tissues—
secondary xylem and secondary phloem –from a vascular cambium.
•Secondary growth in roots also involves in the formation of periderm, composed mostly
of cork tissue, from a cork cambium.
•Commonly, the roots of monocots lack secondary growth and, hence, consist entirely of
primary tissues.
Root development in a woody eudicot.
(a) Early stage in primary development, showing primary meristems.
(b) At the completion of primary growth, showing the primary tissues and the
meristematic procambium between the primary xylem and primary phloem.
(c) Origin of vascular cambium.
(d) After formation of some secondary phloem and additional secondary xylem, which
further separate the primary phloem from the primary xylem. A periderm has not yet
formed.
(e) After formation of additional secondary xylem and secondary phloem and of periderm.
(f) At end of first year's growth, showing the effect of secondary growth--including
periderm formation--on the primary plant body. In (d) through(f), the radiating lines
represent rays.
•Transverse sections of the willow (Salix) root, which becomes woody. (a) Overall
view of root near completion of primary growth.
•Transverse sections of the willow (Salix) root, which becomes woody. (b) Detail of
primary vascular cylinder.
•Transverse sections of the willow (Salix) root, which becomes woody. (c) Overall
view of root at end of first year's growth, showing the effect of secondary growth on
the primary plant body.
Origin of Lateral Roots
Root pericycle cell dedifferentiates to form a root primordium.
Root pushes out through stele, cortex and epidermis by root cap secretions. Eventually
the vascular tissue of the lateral root is joined to the vascular tissue of the “parent” root to
permit continuous flow of substances.
45
Three stages in the origin of lateral roots in a willow (Salix). (a) One root primordium
is present (below) and two others are being initiated in the region of the pericycle
(arrows). The vascular cylinder is still very young. (b) Two root primordia penetrating
the cortex. (c) One lateral root has reached the outside, and the other is about to break
through.
Aerial Roots and Air Roots
Aerial roots of an epiphytic orchid(Oncidium sphacelatum) can absorb moisture from the
air.
 Ficus benghalensis Indian banyan tree
 Many of the Ohia trees （桃金娘）have aerial roots. The aerial roots grow
during times of stress (like volcanic eruptions) and allow the tree gather more
nutrients.

Adaptation for food storage
Large storage root and palmately-divided leaf of the cassava plant (Manihot esculenta)
（木薯）, a member of the diverse Euphorbia Family (Euphorbiaceae)
Transverse sections of the root of a sweet potato (Ipomoea batatas). (a) Overall view.
(b) Detail of xylem, showing cambium around vessels. Most of the xylem and phloem is
composed of storage parenchyma cells.
Transverse section of a sugarbeet (Beta vulgaris) root, with supernumerary cambia
indicated by arrows on the diagram. The original vascular cambium produces relatively
little secondary xylem and secondary phloem (in the center of the root).
Summary of root development in a woody eudicot during the first year of growth
Primary meristem
Primary tissues
Protoderm
Epidermis
Apical
Ground meristem
Cortex
Meristem
Procambium
Vascular cylinder:
Secondary tissues
Cork
Pericycle
Cork cambium
Phelloderm
Undifferentiated
procabium
Vascular
Secondary
phloem
cambium
Secondary
xylem
Primary phloem
Primary xylem
46
Chapter 6 The Shoot: Primary Structure and Development
In this Chapter we’ll study the following topics:
•
•
•
•
•
•
•
•
Origin and Growth of the Primary Tissues of the Stem
Primary Structure of the Stem
Relation between the Vascular Tissues of the Stem and the Leaf
Morphology of the Leaf
Structure of the Leaf
Grass Leaves
Leaf Abscission
Stem and Leaf Modifications .
By the time you finish studying this, you should be able to answer the following
questions:
1. What is the structure of the shoot apical meristem of angiosperms, and what
is the relationtionship between the zones of that meristem and the primary
meristems of the shoot?
2. What three basic types of organization are found in the primary structure of
the stems of seed plant?
3. What are leaf traces, and how are they indicative of the intimate relationship
that exists between the stem and the leaf? What hypothesis have been
proposed to explain the pattern of leaf arrangement on stems?
4. What structural differences exist between the leaves of monocots and those of
other angiosperms?
 A portion of a Croton（巴豆） shoot.
The leaves of Croton, a eudicot, have a mottled appearance due to clonal variations in the
ability of leaf cells to produce chlorophyll and are spirally arranged along the stem. At
the apex the leaves are so close together that nodes and internodes are not distinguishable
as separate regions of the stem. Growth in length of the stem between successive leaves,
which are attached to the stem at the nodes, results in formation of the internodes.
 Origin and Growth of the Primary Tissues of the Stem
Longitudinal section of shoot tip of the common houseplant Coleus blumei（锦紫
苏）, a eudicot. The leaves in Coleus are arranged opposite one another at the nodes,
each successive pair at right angles to the previous pair (decussate phyllotaxy); thus
the leaves of the labeled node are at right angles to the plane of section.

The apical meristem at the tip of the shoot is protected by young leaves that
fold over it, as seen in this longitudinal section of a eudicot shoot.
Activity of the apical meristem, which repetitively produces leaf and bud primordia,
results in a succession of repeated units called phytomeres. Each phytomere consists of a
node with its attached leaf, the internode below that leaf, and the bud at the base of the
47
internode. The boundaries of the phytomeres are indicated by the dashed lines. Note that
the internodes are of increasing length the farther they are from the apical meristem.
Internodal elongation accounts for most of the increase in length of the stem.

Tunica-corpus organization. (a), (b) Detail of a Coleus blumei（锦紫苏）
shoot apex. Coleus has a two-layered tunica, represented by the L1 and L2 layers
of the apical meristem. The initial layer of the corpus is represented by the L3
layer. The corpus corresponds to the central mother cell zone. (c) Anticlinal and
periclinal divisions. Cell divisions in the tunica layers are almost exclusively
anticlinal. Those in the initial layer of the corpus are both anticlinal and periclinal.
By dividing periclinally, the cells of the initial layer of the corpus add cells to the
corpus.

Diagrammatic representation of the anatomy of the top, or crown, of a thickstemmed monocot without secondary growth, such as a palm tree. Increase in
thickness is due to meristematic activity below the young leaf bases. The apical
meristem and youngest leaf primordia are conventional in size, although they
appear sunken below broad stem tissues. The zone of procambium formation is
called the meristematic cap.

Stem with buds and 3-year old shoot with buds.
 Primary Structure of the Stem
Considerable variation exists in the primary structure
of stems of seed plants, but three basic types of organization can be recognized:
1. The vascular system of the internode appears as a more or less continuous
cylinder within the ground tissue(conifers, magnoliids, and eudicots).
2. The primary vascular tissues develop as a cylinder of discrete strands, or bundles,
separated from one another by ground tissue.
3. In the stems of most monocots and of some herbaceous eudicots, the vascular
bundles occurs in more than one ring of bundles or appear scattered throughout
the ground tissue.

The three basic types of organization in primary structure of stems as seen in
transverse section. (a) The vascular system appears as a continuous hollow
cylinder around the pith. (b) Discrete vascular bundles form a single ring around
the pith. (c) The vascular bundles appear scattered throughout the ground tissue.
The primary vascular tissues of the Tilia stem form an almost continuous vascular
cylinder
a) Transverse section of basswood (Tilia americana) stem in a primary stage of
growth. The vascular tissues appear as a continuous hollow cylinder that divides
the ground tissue into pith and cortex.
b) Detail of a portion of the same basswood stem.
48

The primary vascular tissues of the Sambucus stem form a system of
discrete strands
Transverse sections of the stem of the elderberry (Sambucus canadensis)（接骨
木） in a primary stage of growth.
(a) A very young stem, showing protoderm, ground meristem, and three discrete
procambial strands. The procambial strand on the left contains one mature sieve element
(upper arrow) and one mature tracheary element (lower arrow).
(b) Primary tissues farther along in development
(c) Stem near completion of primary growth. Fascicular and interfascicular cambia are
not yet formed.


The stems of Medicago and Ranunculus are herbaceous
Transverse section of stem of alfalfa(Medicago sativa)（苜蓿）, a eudicot with
discrete vascular bundles(middle) and detail of a portion of the same alfalfa
stem(right)
 A closed vascular bundle. Transverse section of vascular bundle of the buttercup
(Ranunculus)（毛茛）, an herbaceous eudicot.
The vascular bundles of the buttercup are closed, that is, all of the procambial
cells mature, precluding secondary growth. The primary phloem and primary xylem are
surrounded by a bundle sheath of thick-walled sclerenchyma cells.


In the Zea stem the vascular bundles appear scattered in transverse section
Stem of maize (Zea mays). (a) Transverse section of the internodal region,
showing numerous vascular bundles scattered throughout the ground tissue. (b)
Transverse section of the nodal region of a young maize stem, showing horizontal
procambial strands that interconnect the vertical bundles. (c) A mature stem split
longitudinally; the ground tissue has been removed to expose the vascular system.

Three stages in the differentiation of the vascular bundles of maize (Zea
mays), as seen in transverse sections of the stem.
(a) The protophloem elements and two protoxylem elements are mature.
(b) The protophloem sieve elements are now crushed, and much of the
metaphloem is mature. Three protoxylem elements are now mature, and the two
metaxylem vessel elements are almost fully expanded
(c) Mature vascular bundle surrounded by a sheath of thick-walled sclerenchyma
cells. The metaphloem is composed entirely of sieve-tube elements and
companion cells. The portion of the vascular bundle once occupied by the
protoxylem elements is now a large space known as the protoxylem lacuna. Note
the wall thickenings of destroyed protoxylem elements bordering the air space.




Diagrams of the primary vascular system in the stem of an elm (Ulmus)（榆树）,
a eudicot. (a) A transverse section of the stem showing the discrete vascular
bundles encircling the pith. (b) Longitudinal view showing the vascular cylinder
as though cut through leaf trace 5 in (a) and spread out in one plane. The
49
transverse section in (a) corresponds with the topmost view in (b). The numbers in
both views indicate leaf traces. Three leaf traces--a median trace and two lateral
traces--connect the vascular system of the stem with that of the leaf. A stem
bundle and its associated leaf traces are called a sympodium.


Relation between the vascular tissues of the stem and the leaf
The relation between branch traces and a leaf trace to the vascular system in the
main stem. Actually, the branch traces are leaf traces--the leaf traces of the first
leaves of the bud or lateral branch. In magnoliids and eudicots, there are
ordinarily two branch traces per bud.
Morphology of the Leaf
1. Simple Leaf: One Blade
2. Compound Leaf: Blade Divided Into Leaflets
•A. Palmately Compound leaf: No Rachis
•B. Pinnately Compound (Pinnate): With A Rachis
•C. Pinnately and Palmately Trifoliate
Left: basket bush (Rhus trilobata)(漆树）, also referred to by the politically incorrect
name of squaw bush; center: poison oak (Toxicodendron diversilobum)（毒葛）; right:
Baja California poison ivy (T. radicans ssp. divaricatum)（常春藤）.
 D. Twice Pinnately Compound leaf (Bipinnate)
 E. Pinnatid: Pinnately Dissected Nearly To The Midrib
 The Hawaiian tree fern (Cibotium glaucum) in Hawaii Volcanoes National Park on
the island of Hawaii. These beautiful native ferns form a dominant understory
component in forests of ohia (Metrosideros polymorpha).
 Sadlera cyatheoides, an endemic Hawaiian fern that commonly grows on lava flows
around Kilauea Crater. On the underside of the smallest leaf divisions (pinnules) is a
brown linear sorus (sporangia cluster). This fern is one of the first plants to colonize
lava flows after an eruption.
 Leaf Arrangement (Phyllotaxy)
Three different leaf arrangements: Alternate (one leaf per node), opposite (two leaves
per node) and whorled (three or more leaves per node). A node is the place where one
or more leaves are attached along the stem. The area between the nodes is called the
internode.
 4. Leaf Venation
Leaf venation in two species of Ceanothus leucodermous (白皮美洲茶）has
glaucous leaves with three main veins from the base. This is a thorny (spiny)
chaparral shrub with rigid, sharp-pointed branchlets. It is common on Palomar
Mountain in San Diego County. C. palmeri（帕麦尔氏美洲茶） has pale green
leaves with one main vein from the base. This shrub is also common on Palomar
Mountain
 5. Leaf Shapes
A. The Prefix "Ob" In A Descriptive Leaf Term
 B. Images Of Leaf Shapes
50

Leaf Apices

7. Leaf Bases

8. Leaf Margins

The pinnately compound leaf of the pea (Pisum sativum).

The pinnately compound leaf of the pea (Pisum sativum). Notice the stipules at the
base of the leaf and the slender tendrils at the tip of the leaf. In the pea leaf, the
stipules are often larger than the leaflets.

Sessile leaves

Sessile leaves (leaves without a petiole) are often found among eudicots, such as
Moricandia, a member of the mustard family (a), but are particularly characteristic of
grasses and other monocots. (b) In maize (Zea mays), a monocot, the base of the leaf
forms a sheath around the stem. The ligule, a small flap of tissue extending upward
from the sheath, is visible. The parallel arrangement of the longitudinal veins is
conspicuous in the portion of the blade shown here.

9.Conifer Leaves


Structure of the Leaf
Sections of lilac (Syringa vulgaris)（西洋丁香） leaf.
(a) A transverse section through a midrib showing the midvein.
b) A transverse section through a portion of the blade. Two small veins (minor veins)
can be seen in this view.
 (c) This is a "paradermal section" of the leaf. Strictly speaking, a paradermal section
is one cut parallel to the epidermis. In practice, such sections are more or less oblique
and extend from the upper to the lower epidermis.
 Sections of lilac (Syringa vulgaris) leaf. (d), (e) Enlargements of portions of (c). (d)
Palisade parenchyma and spongy parenchyma with a vein ending, sectioned through
some tracheary elements and surrounded by a bundle sheath. (e) A portion of the
lower epidermis with two trichomes (epidermal hairs) and several stomata.

Transverse section of a leaf of the water lily (Nymphaea odorata), a magnoliid,
which floats on the surface of the water and has stomata in the upper epidermis only.
As is typical of hydrophytes, the vascular tissue in the Nymphaea leaf is much
reduced, especially the xylem. The palisade parenchyma consists of several layers of
cells above the spongy parenchyma. Note the large intercellular (air) spaces, which
add buoyancy to this floating leaf.

Transverse section of oleander(Nerium oleander)(欧洲夹竹桃） leaf. Oleander is
a xerophyte, and this is reflected in the structure of leaf. Note the very thick cuticle
51
covering the multiple(several-layered) epidermis on the upper and lower surfaces of
the leaf. The stomata and trichomes are restricted to invaginated portions of the lower
epidermis called stomatal crypts.


1. The leaf surface of a species of Tradescantia(紫露草）, also known as
spiderwort (Commelinaceae)。 Note the paired guard cells and stoma (opening slit)
between them (circled in red). Also note the scattered hairs (trichomes).
2. Microscopic view of the paired guard cells and stoma on the leaf surface of
spiderwort (Tradescantia). An opening or stoma develops between the inflated
(turgid) guard cells due to a differential thickening of their walls.

Stomatal crypt. Scanning electron micrographs of a stomatal crypt in the lower
epidermis of an oleander (Nerium oleander)（夹竹桃） leaf.
(a) Lower-magnification view of a crypt, showing numerous trichomes lining the
crypt.
(b) A higher magnification showing one of the stomata (arrow), which are restricted to
crypts.

Stomata, shown in scanning electron micrographs. (a) Potato (Solanum tuberosum)
leaf, showing the random arrangement of stomata typical of the leaves of eudicots.
The guard cells in potato are crescent-shaped and are not associated with subsidiary
cells. (b) Maize (Zea mays) leaf, showing the parallel arrangement of stomata typical
of the leaves of monocots. In maize each pair of narrow guard cells is associated with
two subsidiary cells, one on each side of the stoma.
Grass Leaves
•Transverse section of sugarcane (Saccharum officinarum) leaf. As is typical of C4
grasses, the mesophyll cells (arrows) are radially arranged around the bundle sheaths,
which consist of large cells containing many large chloroplasts.
•Transverse section of wheat (Triticum aestivum) leaf. As is typical of C3 grasses, the
mesophyll cells are not radially arranged around the bundle sheaths. The bundle sheaths
in the wheat leaf consist of two layers of cells: an outer sheath of relatively thin-walled
parenchyma cells and an inner sheath, the mestome sheath, of thick-walled cells.
•Transverse sections of a leaf of annual bluegrass (Poa annua)(早熟禾）, a C3 grass.
Portions of (a) folded and (b) unfolded leaves including midvein. In the grass leaf, the
mesophyll is not differentiated as palisade and spongy parenchyma. Strands of
sclerenchyma cells commonly occur above and below the veins. The epidermis of the
grass leaf contains bulliform cells--large epidermal cells thought to play a part in the
folding and unfolding of grass leaves. In the Poa leaf shown in (a), the bulliform cells
located in the upper epidermis are partly collapsed and the leaf is folded. An increase in
turgor in the bulliform cells would presumably cause the leaf to unfold (b).
Leaf Abscission
•Abscission
52
•Deciduous plants drop their leaves seasonally.
•Occurs as a result of changes in an abscission zone near the base of the petiole of each
leaf.
•Cells of the protective layer become coated and impregnated with suberin.
•Stem and Leaf Modification
•Stem and leaf may undergo modification and perform functions quite different from
those commonly associated with these two components of the shoot.
•Tendril - coiled clawed structure that enables plants to attach to objects. Tendrils
are modified leaves and stems.
•Thorn - Woody, sharp-pointed stem. These can be terminal or in the axil of leaves.
They are sometimes branched.
•Spine - Modified leaf or leaf-parts. Cacti spines are modified leaves
•Prickle - Sharp structure that is an outgrowth of the bark or epidermis
53
Chapter 7 Secondary Growth in Stems
In this Chapter we’ll deal with the following topics:
• Annuals, Biennials, and Perennials
• The Vascular Cambium
• Effect of Secondary Growth on the Primary Body of the Stem
• The Wood: Secondary Xylem
By the time you finish studying this chapter, you should be able to answer the
following question:
1. How do annuals, biennial, and perennials differ?
2. What types of cells make up the vascular cambium, and how do these cells
function?
3. How does secondary growth affect the primary body of stem?
4. What tissues are produced by the cork cambium, and what is the function of
periderm?
5. What is bark, and how does its composition change during the life of a woody
plant?
6. What is wood, and how does conifer wood differ from angiosperm wood?
•A solitary shagbark hickory (Carya ovata)(小糙皮山核桃） in the summer condition.
Plants have been able to achieve such great stature because of the ability of their roots
and stems to increase in girth, that is, to undergo secondary growth. Most of the tissue
produced in this manner is secondary xylem, or wood, which not only conducts water and
minerals to the far reaches of the shoot but also provides great strength to the roots and
stems.
•Secondary growth
secondary growth Cells in a plant that are produced by a cambium. Increase in girth of a
plant due to the action of lateral meristems such as the vascular cambium and the cork
cambium. The main cell produced in secondary growth is secondary xylem, better known
as wood.
•Annuals, Biennials, and Perennials
•Annual plant: a plant which grows, produces seeds, and dies within one year.
•Biennial plant: a plant that lives for two years, producing seeds and flowers in its
second year.
•Perennial plant: a plant that lives for several years.
•Corn (Zea mays) is an annual plant, since it completes its life cycle in one growing
season, within one year or less. Seeds germinate, plants grow to reproductive maturity,
flower, produce seeds, and then die. Annual plants are usually herbaceous.
54
•Carrot (Daucus carota ) is a biennial plant: it completes its life-cycle in two growing
seasons (within two years). Germination and vegetative growth take place during the first
year, with food storage in underground parts of the plant for over-wintering. In the case
of carrot, resources are stored in a swollen root.
•Here is a flowering plant of carrot. During the second season, a biennial plant grows to
reproductive maturity, flowers, produces seeds, and dies. Biennial plants are usually
herbaceous. These are plants of wild carrot (Daucus carota) in flower.
•A perennial plant is a plant that lives for two or more growing seasons (from several
years to several centuries). It can be either herbaceous or woody. Some perennial plants
can flower during their first year, while others live many years before reaching
reproductive maturity
•A: Onion bulb B: Crocus corm C: Potato tuber D: Iris rhizome
The Vascular Cambium
•The meristematic cells of Vascular Cambium exist in two forms: as vertically oriented
fusiform initials , and as horizontally oriented ray initials.
•Secondary xylem and secondary phloem are produced through periclinal divisions of
the cambial initials and their immediate derivatives.
•The xylem and phloem cells produced by the fusiform initials have their long axes
oriented vertically and make up what is known as the axial system of the secondary
vascular tissues.
•The ray initials produce horizontally oriented ray cells, which form the vascular rays or
radial system.
•Vascular cambium of the apple (Malus sylvestris) tree, seen here in tangential view.
Tangential sections are cut at right angles to the rays, so we see the rays here in
transverse section. A cambium such as this, in which the fusiform initials are not
arranged in horizontal tiers on tangential surfaces, is said to be nonstoried. The fusiform
initials average 0.53 millimeter in length in the apple.
•Vascular cambium of the black locust (Robinia pseudoacacia)(洋槐） tree, seen
here in tangential view. A cambium such as this, in which the fusiform initials are
arranged in horizontal tiers on tangential surfaces, is said to be storied. The fusiform
initials average 0.17 millimeter in length in black locust.
•Periclinal and anticlinal divisions of fusiform initials. (a) Periclinal divisions are
involved in the formation of secondary xylem and secondary phloem cells, and result in
the formation of radial rows of cells. When an initial divides periclinally, the two
daughter cells appear one behind (or in front of) the other. (b) Anticlinal divisions are
involved in the multiplication of fusiform initials. When an initial divides anticlinally, the
two daughter cells appear side by side.
55
•Diagram showing the relationship of the vascular cambium to its derivative tissues-secondary xylem and secondary phloem. The darker cells are the more recently
derived ones. The vascular cambium is made up of two types of cells--fusiform initials
and ray initials--which form the axial and radial systems, respectively. The arrangement
of the cambial initials determines the organization of the secondary vascular tissues.
•Effect of secondary growth on the primary body of the stem
•Stem development in a woody angiosperm.
•(a) Early stage in primary development, showing primary meristems.
•(b) At completion of primary growth.
•(c) Origin of vascular cambium.
•(d) After formation of some secondary xylem and secondary phloem.
•(e) At end of first year's growth, showing the effect of secondary growth--including
periderm formation--on the primary plant body. In (d) and (e), the radiating lines
represent rays.
•Transverse section of an elderberry (Sambucus canadensis) stem in which a small
amount of secondary growth has taken place. A cork cambium has not yet formed.
•Transverse section of an elderberry (Sambucus canadensis) stem at the end of the
first year's growth.
•Tilia americana
Cross section through a one year old stem of a basswood(left).
Cross section through a two year old stem of a basswood(right).
•Three-Year Tilia Stem Cross Section
•Six-year Tilia Stem Cross Section
•Details of the stem of basswood.
•Closeup of a cross-section of basswood growth ring. Note the growth ring, which is
formed by very small cells followed by large cells with the commencement of growth in
the next growing season.
•Balsa Wood（美国的一种轻质木材）（Corkwood) (cross section) Showing Large
Conductive Elements (SEM x220).
•The Periderm is the dermal tissue system of the secondary plant body
•Some stages of periderm and lenticel development in elderberry (Sambucus canadensis),
as seen in transverse sections.
•(a) Newly formed periderm, which consists of cork cambium, cork, and phelloderm, is
seen beneath the epidermis. The epidermis has been separated from the cortex, consisting
of collenchyma and parenchyma, by the periderm.
•(b) Periderm in more advanced stage of development, with increase in size of cork layer.
Note that the epidermis is degenerating.
•(c) Initiation of a lenticel. Collenchyma cells of the cortex can be seen beneath the
developing lenticel.
56
•d) Well-developed lenticel. The phelloderm in Sambucus generally consists of a single
layer of cells.
•The lenticels allow gas exchange though the periderm, the above picture shows lenticel
of the stem of Dutchman‘s pipe (Aristolochia)(马兜铃）, as seen in transverse section.
Unlike that of Sambucus, the phelloderm of Aristolochia consists of several layers of
cells.
•The bark includes all tissues outside the vascular cambium
Diagram of part of a red oak (Quercus rubra) stem, showing the transverse, tangential,
and radial surfaces. The dark area in the center is heartwood. The lighter part of the wood
is sapwood.

Transverse section of the bark and some secondary xylem from an old stem of
basswood (Tilia americana). Several periderms (arrows) can be seen traversing the
mostly brownish outer bark in the upper third of the section. Below the outer bark is
the inner bark, which is quite distinct in appearance from the more lightly stained
secondary xylem in the lower third of the section.

Transverse section of the bark of a black locust (Robinia pseudo-acacia)（洋槐）
stem, consisting mostly of nonfunctional phloem.
Transverse section of secondary phloem of the black locust (Robinia pseudo-acacia),
showing mostly functional phloem. Sieve tubes (indicated by arrows) of the
nonfunctional phloem have collapsed.
Radial section of the bark of black locust (Robinia pseudo-acacia). Most of the
section consists of nonfunctional phloem, in which the sieve tubes are collapsed
(arrows). In black locust, the functional phloem consists only of the current season's
growth increment, which becomes nonfunctional in late autumn when its sieve tubes
die and collapse.
Bark of four species of trees. (a) Thin, peeling bark of the paper birch (Betula
papyrifera)(纸皮桦）. Horizontal lines on the surface of the bark are lenticels. (b)
Shaggy bark of the shagbark hickory (Carya ovata)（小糙皮山核桃）. (c) Scaly
bark of a sycamore, or buttonwood (Platanus occidentalis)（美国梧桐）. (d) Deeply
furrowed bark of the black oak (Quercus velutina) （美洲黑栎）.




The Wood: Secondary xylem
Conifer wood lacks vessel
Block diagram of the secondary xylem of white pine (Pinus strobus)（美国五针松）, a
conifer. With the exception of the parenchyma cells associated with the resin ducts, the
axial system consists entirely of tracheids. The rays are only one cell wide, except for
those containing resin ducts.

Wood of white pine (Pinus strobus)(美国五针松）, a conifer, in (a) transverse, (b)
radial, and (c) tangential sections.
57
 Details of white pine (Pinus strobus) wood.
(a) Transverse section, showing bordered pit-pairs on radial walls of tracheids.
(b) Radial section, showing the face view of bordered pit-pairs in walls of tracheids.
(c) Tangential section, showing bordered pit-pairs of tracheids.
(d) Radial section, showing ray.
The rays of pine and other conifers are composed of ray tracheids and ray parenchyma
cells. Here ray tracheids occur at the top and bottom of the ray and ray parenchyma cells
in the middle. Notice the bordered pits of ray tracheids. Above the ray parenchyma are
two adjacent bordered pit-pairs
Angiosperm woods typically contain vessels
•Growth layers of wood, in transverse sections.
•(a) Red oak (Quercus rubra). The large vessels of ring-porous wood such as red oak are
found in the early wood. The dark vertical lines are rays.
•(b) Tulip tree (Liriodendron tulipifera)（美国鹅掌楸）, a diffuse-porous wood.




Wood of red oak (Quercus rubra) in
(a) transverse,
(b) radial,
and (c) tangential sections.
Sapwood conducts and heartwood does not
•Tyloses(侵填体） are balloonlike outgrowths of parenchyma cells that partially or
completely block the lumen of a vessel.
•(a) Transverse and (b) longitudinal sections showing tyloses in vessels of white oak
(Quercus alba), as seen with a light microscope.
Growth rings result from the periodic activity of the vascular cambium
•Annual rings in wood each represent one year's increment of growth. The number of
rings varies with the distance above ground, the oldest part of the trunk occurring at
ground level.
•(a) Diagram of a median longitudinal section of a tree trunk,
•and (b) transverse sections taken at four different levels. Once secondary growth has
begun in a portion of stem (or root), that portion no longer increases in length.

“FOREST OF ANCIENTS” - home of the Great Basin Bristlecone Pine (Pinus
longaeva)(狐尾松）
•Some of these trees are more than 4,000 years of age. Bristlecone Pines have survived in
spite of, and perhaps because of, their harsh environment at White Mountains, California.
These trees do not live in isolation, but are interconnected to other living and non-living
things and to each other.

Summary of stem development in a woody angiosperm during the first year of
growth
58
Chapter 8 Systematics: The Science of Biological Diversity
In this Chapter we’ll deal with the following topics:
•
•
•
•
•
•
•
Taxonomy and Hierarchical Classification
Classification and Phylogeny
Methods of Classification
Molecular Systematics
The Major Groups of Organisms: Bacteria, Archaea, and Eukarya
Origin of the Eukaryotes
The Eukaryotic Kingdoms
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What is the binomial system of nomenclature?
2. Why is the term hierarchical used to describe taxonomic categories, and
what are the principal categories between the levels of species and kingdom?
3. What is cladistic analysis, and how is a cladogram constructed?
4. What evidence is there for the existence of the three major domains, or
groups, of living organisms?
5. What are the four kingdoms of eukaryotes, and what are the major
identifying characteristics of each?
What is systematics?
•Systematics is the study of the historical relationships of groups of biological organisms
-- the recognition and understanding of biodiversity.
•Systematics includes the processes of identifying the basic systematic unit (the species),
discovering the patterns of relationships of species at successively higher levels, building
classifications based on these patterns and naming appropriate taxa (taxonomy), and the
application of this pattern knowledge to studying changes in organismal features through
time.
•In one word, the scientific study of biological diversity and its evolutionary history is
called systematics.
Taxonomy and Hierarchical Classification
•Taxonomy is the branch of biology dealing with the identifying , naming and classifying
of species.
•The ancient Greek philosopher Aristotle apparently began the discussion on taxonomy.
•During the 1700s, Swedish botanist Carl Linnaeus classified all then-known organisms
into two large groups: the kingdoms Plantae and Animalia.
59
•Robert Whittaker in 1969 proposed five kingdoms: Plantae, Animalia, Fungi, Protista,
and Monera.
•Other schemes involving an even greater number of kingdoms have lately been proposed,
however most biologists employ Whittaker's five kingdoms.
•Recent studies suggest that three domains be employed: Archaea, Bacteria, and Eukarya.
•Taxonomy of a selected plant species. Note the increasing inclusively of the "higher"
taxonomic ranks. Kingdoms have a great deal more types of creatures in them than do
species.
The Species name consists of the Genus name plus the specific epithet
•Linnaeus attempted to classify all known species of his time (1753). Linnaeus
hierarchical classification was based on the premise that the species was the smallest unit,
and that each species (or taxon) nested within a higher category.
•Linnaeus also developed the concept of binomial nomenclature, whereby scientists
speaking and writing different languages could communicate clearly.
•Carl Linnaeus is often called the Father of Taxonomy. His system for naming, ranking,
and classifying organisms is still in wide use today (with many changes). His ideas on
classification have influenced generations of biologists during and after his own lifetime.
•In 1753, Linnaeus published a two-volume work entitled Species Plantarum(The Kinds
of Plants) in which he described each species in Latin by a sentence limited to twelve
words—Polynomial(devised earlier by Caspar Bauhin, 1560-1624).
•First person who called Nepeta cataria(catnip)(猫薄荷) for Nepeta floribus interrupte
spicatus pendunculatis
The Species Name Consists of the Genus Name Plus the Specific Epithet-Binomial
Nomenclature
•In biology, binomial nomenclature is a standard convention used for naming species.
• As the word 'binomial' suggests, the scientific name of a species is formed by the
combination of two terms: the genus name and the species epithet or descriptor.
•The first term (generic name) is always capitalized, while the specific epithet is not; both
are to be typeset in italics, e.g. Laminaria japonica.
•The genus name can be abbreviated to its initial letter (as L. japonica) when repeated or
when several species from the same genus are being listed or discussed in the same paper
or report.
• In rare cases this abbreviation form has spread to more general use—for example the
bacterium, Escherichia coli, is often referred to as just E. coli.
Value and use of the binomial system
•The value of the binomial system derives primarily from its economy and its widespread
use:
•the same name is used in all languages, avoiding difficulties of translation;
•every species can be unambiguously identified with just two words;
•the system has been adopted internationally in botany (since 1753), zoology (since 1758)
and bacteriology (since 1980).
60
Extensions on the binomial name
•Trinomial nomenclature
•When a species is further subdivided, a trinomial nomenclature is used.
•In botany, a species can be further divided into any of subspecies, variety, or form,
whereas in zoology, a species is only subdivided into subspecies.
•Trinomial names of plants therefore usually include a qualifier (such as "subvar." in the
example above), whereas trinomial names of animals never do.
Authorship in scientific names
•A complete reference to a species includes not only the genus and species, but the
author(s) that described the species and gave it a name.
• This addition of authorship is usually only done once in a particular article or citation.
And the name or names are usually abbreviated if possible: Helianthus annuus L.（向
日葵） where "L." refers to Linnaeus.
•Amygdalus persica L. (桃）
•Prunus persica (L.) Batsch
Definitions of species
•A morphological species is a group of organisms that have a distinctive form:
•Species have been defined in this way since well before the beginning of recorded
history. Although much criticised, the concept of morphological species remains the
single most widely used species concept in everyday life, and still retains an important
place within the biological sciences, particularly in the case of plants.
•The biological species or isolation species concept identifies a species as a set of
actually or potentially interbreeding organisms.
•The key to defining a biological species is that there is no significant cross-flow of
genetic material between the two populations.
Type specimen
•Each species has a type specimen, usually a dried plant specimen housed in a museum or
herbarium,which is designated either by the person who originally named that species or
by a subsequent author if the original author failed to do so.
•The type specimen serves as a basis for comparison with other specimen in determining
whether they are members of the same species.
•Type specimen of the angiosperm Podandrogyne formosa(family Capparidaceae)（白花
菜科）, found in Costa Rica and westen Panama. This specimen was collected by
Theodore S. Cochrane and described by him in a paper published in the journal Britonnia.
The members of a species may be grouped into subspecies or varieties
•Subspecies:
61
In taxonomy, a subspecies is the taxon immediately subordinate to a species.
Members of one subspecies differ morphologically from members of other
subspecies of the species
•Variety (biology):
A variety is a recognised division of a species, especially in botany; in zoology,
species are divided into subspecies rather than varieties , e.g Prunus persica var.
nectarina (油桃）
International Code of Botanical Nomenclature(ICBN)
•International Code of Botanical Nomenclature (ICBN) governs the naming of plants. Six
principles form the basis of the code:
•1. Botanical nomenclature is independent of zoological nomenclature.
•2. The application of names of taxonomic groups is determined by the means of
nomenclatural types, a specimen.
•3. Nomenclature of taxonomic groups is based on priority of publication.
•4. Each taxonomic group can have only one correct name, the earliest that is in
accordance with the rules (some exceptions).
•5. Scientific names are latinized.
•6. The rules are retroactive (some exceptions).
Organisms are grouped into broader taxonomic categories arranged in a hierarchy
•Taxon
A taxon (plural taxa) is an element of a taxonomy, e.g. in the scientific classification in
biology. Taxa form a hierarchical scheme, each being broken down into subtaxa. In
traditional Linnaean taxonomy, taxa are ranked as follows:
Kingdom
•Phylum (animals) or Division (plants)
•Class
•Order
•Family
• Tribe
•Genus
•
Section
•
Series
•Species
•
Variety
•
Form
•A prefix is used to indicate a ranking that falls between two taxa. The prefix superindicates a rank above another, the prefix sub- indicates a rank below another, and
the prefix infra- indicates a rank below sub-.
The place of Laminaria japonica in the system
•Plantae
• Phaeophyta
•
Phaeosporeae
•
Laminarials
62
•
•
•
Laminariaceae
Laminaria
Laminaria japonica Aresch
Methods of classification
•The traditional methods is based on a comparison of outward similarities.
•The evolutionary history of a group of related organisms can be represented by a
phylogenetic tree constructed by using traditional methods. The vertical locations of the
branching points indicate when particular taxa diverged from one another. The horizontal
distances indicate how much the taxa have diverged, taking into account a number of
different characteristics.
The cladistic methods is based on phylogeny
•The most widely used method of classifying organisms today is known as cladistics, or
phylogenetic analysis.
•The result of cladistic analysis is a cladogram, which provides a graphical representation
of a working model, or hypothesis, of branching sequences.
Selected Characters Used in Analyzing the Phylogenetic Relationships of Four Plant
Taxa
Characters
Taxon
Xylem and
Phloem
Wood
Seeds
Flowers
Mosses
Ferns
+
Pines
+
+
+
Oaks
+
+
+
+
•Cladograms
showing phylogenetic relationships between ferns, pines, and oaks, indicating
the shared characters that support the patterns of relationships. (a) A cladogram based on the
presence or absence of xylem and phloem. (b) Further resolution of the relationships, based
on additional information regarding the presence or absence of wood, seeds, and flowers.
•
Molecular Systematics
•A
Comparison of Amino Acid Sequences Provides a Molecular Clock.
•The
use of amino acid sequences of homologous proteins to determine evolutionary relationships.
This method assumes that the greater the number of amino acid differences between homologous
63
proteins of any two organisms, the more distant their evolutionary relationship. Conversely, the fewer
the differences, the closer their relationship.
A Comparison of Nucleotide Sequences Provides Evidence for Three Domains of Life
•A
universal evolutionary tree as determined by comparing sequences of ribosomal RNA. The data
support the division of the living world into three domains, two of which consist of prokaryotic
organisms (Bacteria and Archaea) and one of eukaryotic organisms (Eukarya).
The Major Group of Organism:
Bacteria, Archaea, and Eukarya
Some Major Distinguishing Features of the Three Domains of Life
Characteristics
Bacteria
Archaea
Eukarya
Cell type
Prokaryotic
Prokaryotic
Eukaryotic
Nuclear envelope
Absent
Absent
Present
Number of chromosomes
1
Chromosome configuration Circular
1
More than 1
Circular
Linear
Organelles(mitochondria
and plastids)
Absent
Absent
Present(in
all but a few)
Cytoskeleton
Absent
Absent
Yes
No
Present
Chlorophyllbased photosynthesis
Yes
Origin of the Eukaryotes
•The
Serial Endosymbiotic Theory Provides a Hypothesis for the Origin of Mitochondria and
Chloroplasts.
•The
Endomembrane System is Thought to Have Evolved from Portions of the Plasma Membrane.
•Mitochondria
and Chloroplasts Are Thought to have Evolved from Bacteria That Were Phagocytized.
•Relationships
within the Eukaryotes Are Not always Well Defined.
•Diagrammatic
representation of the origin of a photosynthetic eukaryotic cell from a heterotrophic
prokaryote.
64
Classification of Living Organisms Included in This Book
Prokaryotic Domains
Bacteria
Bacteria
Archaea
Archaea
Eukaryotic Domain
Eukarya
Kingdom Fungi
Phylum Chytridiomycota(chytrids)
Phylum Zygomycota(zygomycetes)
Phylum Ascomycota(ascomycetes)
Phylum Basidiomycota
Kingdom Protista Heterotrophic Phylum Myxomycota
protists
Phylum Dictyosteliomycota
Phylum Oomycota
Photosynthetic
protists(algae)
Phylum Euglenophyta
Phylum Crytophyta
Phylum Rhodophyta
Phylum Dinophyta
Phylum Haptophyta
Phylum Bacillariophyta
Phylum Chrysophyta
Phylum Phaeophyta
Phylum Chlorophyta
Kingdom Plantae Bryophytes
Phylum Hepatophyta
Phylum Anthocerophyta
Phylum Bryophyta
65
Vascular plants
Seedless vascular plants
Phylum Psilotophyta
Phylum Lycophyta
Phylum Sphenophyta
Phylum Pterophyta
Seed plants
Phylum Cycadophyta
Phylum Ginkgophyta
Phylum Coniferophyta
Phylum Gnetophyta
Phylum Anthophyta
The Eukaryotic kingdoms
•The
Kingdom Protista Includes Unicellular, Colonial, and Simple Multicellular Eukaryotes.
•The
Kingdom Animalia Includes Eukaryotic, Multicellular Ingesters.
•The
Kingdom Fungi Includes Eukaryotic, Multicellular Absorbers.
•The
kingdom Plantae Includes Eukaryotic, Multicellular Photosynthesizer.
Protists.(a) Plasmodium of a plasmodial slime mold, Physarum(phylum Myxomycota), growing on a
leaf.
(b) Postelsia palmiformis, the sea palm(Phaeophyta), growing on exposed intertidal rocks off
Vancouver Island.(c) Volvox, a motile colonial green alga(Chlorophyta).(d) a red alga. (e) A pennate
diatom.
•Fungi.
(a) Red blanket Lichen(Herpothallon sanguineum) growing on a tree trunk.(b) A white coral
fungus(Family Clavariaceae).(c) Mushrooms (genus probably Mycena), with dew droplets, growing
in a rainforest in Peru. (d) An earthball, Scleroderma aurantium(马勃）.
66
Chapter 9 Prokaryotes
In this chapter we’ll deal with the following topics:
•Characteristics
•Diversity
of the Prokaryotic Cell
of Form
•Endospores
•Introduction
to the Cyanobacteria
By the time you finish studying this chapter, you should be able to answer the following
questions:
1. What is the basic structure of a prokaryotic cell?
2. How do prokaryotes reproduce, and in what ways does genetic recombination
take place in prokaryotes?
3. In what way are the cyanobacteria ecologically important?
4. Physiologically, what are the three large groups of Archaea?
Characteristics of the Prokaryotic Cell
•1.
nuclear body
a. Not bounded by a nuclear membrane .
b. Usually contains one circular chromosome composed of deoxyribonucleic acid (DNA)
associated with histone-like proteins.
c. No nucleolus.
d. Nuclear body is called a nucleoid.
2. Cell division
a. Usually by binary fission. No mitosis.
b. Organisms are haploid. No meiosis needed.
3.Plasma membrane
67
a. Cytoplasmic membrane is a fluid phospholipid bilayer without carbohydrates and
usually lacking sterols . Many bacteria do contain sterol-like molecules called hopanoids.
b. Incapable of endocytosis and exocytosis.
4. cytoplasmic structures
a. 70S ribosomes composed of a 50S and a 30S subunit .
b. Internal membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi
apparatus, vacuoles, and lysosomes are absent.
b. No chloroplasts. Photosynthesis usually takes place in infoldings or extensions derived
from the cytoplasmic membrane.
c. No mitotic spindle.
d. No cytoskeleton.
The 70S prokaryotic ribosome consists of a 50S and a 30S subunit. "S" refers to a unit of
density called the Svedberg unit.
•6.
Cell wall
a. Most Eubacteria have cell walls composed of peptidoglycan.
b. The Archaebacteria have cell walls composed of protein, a complex carbohydrate, or
unique molecules resembling but not the same as peptidoglycan.
7. Locomotor organelles
Some have flagella, each composed of a single, rotating fibril and not surrounded by a
membrane. No cilia.
8. Representative organisms
Bacteria (Eubacteria and Archaebacteria)
Diversity of Form
•The
three major forms of prokaryotes are: bacilli, cocci, and spirilla.(a) Clostridium
botulinum, the source of the toxin that causes deadly food poisoning, or botulism, is a
bacillus, or rod-shaped bacterium.
68
•(b)
Many prokaryotes, such as Micrococcus luteus, shown here, take the shape of spheres.
Among the cocci are Streptococcus lactis, a common milk souring agent and Nitrosococcus
nitrosus, a soil bacterium that oxidizes ammonia to nitrites.
Spirilla, such as Magnetospirillum magnetotacticum , are less common than bacilli and
cocci.Flagella can be seen at either end of this cell, which was isolated from a swamp. The
string of dark magnetic particles orient the cell in the Earth’s magnetic field.
Endospores
•Endospores
are extremely tough and thick-walled capsules that can withstand almost any
bad conditions(including outer space), when conditions improve, the endospores come back
to life.
Introduction to the Cyanobacteria (Blue-green algae)
Cyanobacteria are important from ecological and evolutionary perspectives.
1.Cyanobacteria are important in the nitrogen cycle. They are one of very few groups of
organisms that can convert inert atmospheric nitrogen into an organic form, such as nitrate or
ammonia.
2. Photosynthetic cyanobacteria have chlorophyll a, together with carotenoids and accessory
pigment-phycobilin (phycocyanin and phycoerythrin).
3.Within the cells of cyanobacteria are numerous layers of membrances-photosynthetic
thylakoids.
4. The main storage product of cyanobacteria is glycogen.
5.Cyanobacteria are believed to have given rise through synbiosis to some eukaryotic
chloroplasts.
6.In biochemical and structural detail, cyanobacteria are especially similar to the chloroplasts
of red algae.
7.Many cyanobacteria produce a mucilaginous envelope, or sheath.
•
Prochlorophytes Contain Chlorophylls a and b and Carotenoids
69
•The form of cyanobacteria:
•Unicellular
•Filaments,
which may break into fragments called hormogonia(藻殖段）.
•Colonies.
•Three
•(a)
common genera of cyanobacteria.
Oscillatoria, in which the only form of reproduction is by means of fragmentation of the
filament.
•(b)
Calothrix(眉藻属）, a filamentous form a terminal heterocyst. Calothrix is capable of
forming akinetes just above the heterocysts
•(c)
Nostoc commune.These cyanobacteria occur frequently in freshwater habitats.
Cyanobacteria Can Live in a wide Variety of Environments
•The
upper temperature limit for growth of any thermophilic eukaryotic organism is about
o
62-65 C.
o
•In contrast to this, some unicellular cyanobacteria can grow at up to 75 C, and some nono
photosynthetic prokaryotes can grow at 100 C or more.
Thermophilic microbes: Yellowstone National Park
A large channel draining from a hot pool, containing carotenoid-rich microorganisms. The
o
temperature of this channel in the foreground is about 60 C. Layers of white-coloured
limestone can also be seen. Note the footprints of buffalo in the foreground. These animals
often seek the warmth of thermal areas in the winter months.
•Left:
Pink, green and brown-coloured microorganisms occupy the thermal gradients in the
o
flowing water (60-100 C).
•Right:
a pool of water that has condensed from a a fumarole (steam/gas vent at top right of
the image), with abundant growth of a green photosynthetic microorganism.
70
•Zones
of microbial growth in water draining into the Yellowstone River from a raised
thermal vent.
•Zonation
of microorganisms in the seep from a hot pool. The temperature gradient decreases
from right to left of the image, where the temperature is low enough to enable plants to grow.
Part of a water seepage from a hot spring, showing carpets of cyanobacteria and other
o
microbial species. The upper temperature limit for growth of cyanobacteria is 70- 74 C.
•
The rim of this pool is colonised by grasses/sedges（莎草） and by monkey flower (Mimulus
guttatus) （多斑沟酸浆）.
Cyanobacteria Form Gas Vesicles, Heterocysts, and Akinetes
•Gas
vesicles:
The structure of cyanobacteria that provides and regulates the buoyancy of the organisms,
thus allowing them to float at certain levels in the water.
•Heterocyst:
A specilized and enlarged cell that are surrounded by thicked cell wall containing large
amounts of glycolipid, which serves to impede the diffusion of oxygen into the cell.
Akinete
A resistant spores in some cyanobacteria, which are enlarged cells surrounded by thickened
envelopes. Akinetes are resistant to heat and drought and thus allow the cyanobacteria to
survive during unfavorable periods.
•
Mycrocystis sp, which can float in the water because of its gas vesicles.
•Aerial
View of a Large Cyanobacterial Bloom
•Filament
of Anabaena(项圈藻属） shows heterocyst and akinetes.
Anabaena and Nitrogen Fixation
Modern-day filamentous cyanobacteria (Anabaena azollae) （项圈藻）from cavities within
the leaves of the ubiquitous water fern (Azolla filiculoides)（满江红）. The larger, oval cells
71
are heterocysts (red arrow), the site of nitrogen-fixation where atmospheric nitrogen (N2) is
converted into ammonia (NH3).
•This
vital process along with nitrification (formation of nitrites and nitrates) and
ammonification (formation of ammonia from protein decay) make nitrogen available to
autotrophic plants and ultimately to all members of the ecosystem.
72
Chapter 10 Algae
In this Chapter we’ll study the following topics:
•
•
•
•
•
•
•
•
Introduction to algae
The distribution of algae
The form of algae
The reproduction and life history of algae
The classification of algae
Brown Algae: Phylum Phaeophyta
Green Algae:Phylum Chlorophyta
Red Algae: Phylum Rhodophyta
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. How are algae of ecological importance?
2. What are the distinctive cellular characteristics of the red
algae? In what ways is the life history of red algae unusual?
3. What are the basic characteristics of brown algae?
4. What characteristics of the green algae have led botanist to
conclude that the green algae are the protest group from
which plants evolved?
5. How about the reproduction of algae? How many types of life
history for algae, and how to distinguish them?
Introduction to algae
•What is phycology?
• Phycology is the science of algae.
•This discipline deals with the morphology, taxonomy, phylogeny, biology, and ecology
of algae in all ecosystems.
The distribution of algae

Kelp forrest up to 50 m hight are the marine equivalent to terrestrial forest; mainly
built by brown algae

Some algae encrust with carbonate, building reef-like structures; cyanobacteria can
form rock-like structures in warm tidal areas: stromatolites .

Algae grow or are attached to animals and serve as camouflage for the animal

Algae live as symbionts in animals such as Hydra（水螅）, corals, or the protozoan
Paramecium (草履虫）
73
 Small algae live on top of larger algae: epiphyte
 Algae in free water: phytoplankton
 Terrestrial algae
•Algae have adapted to life on land and occur as cryptobiotic（隐生的） crusts in desert
and grassland soils.
Algae live on the snow cover of glaciers.

A symbiosis of algae and fungi produced the lichens, which are pioneer plants,
help convert rock into soil by excreting acids, stabilizing desert soil, are sensitive
to air pollution.
Harmful Algal Blooms (Red Tide)
 Algae can be so dominant that they discolor the water
 Higher amounts of nutrients are ususally the cause
 Algal blooms can have harmful effects on life and ecosystem:
 Reduced water clarity causes benthic communities (seegrass) to die off
 Fish kills are common effects
 50% of algal blooms produce toxins harmful to other organisms, including
humans
 Algal blooms produce a shift in food web structure and species composition
 Algal blooms can mostly be linked to sewage input or agricultural activities,
leading to nutrient pollution: eutrophication (富营养化）
The relationship between red tide and marine ecosystem
Forms of Algae
•Unicell: single cell, motile or nonmotile.
•Colonies: Assemblage of individual cells with variable or constant number of cells that
remain constant throughout the colony life
•Coenobium（定形群体）: Colony with constant number of cells, which cannot survive
alone.
•Filaments: daughter cells remain attached after cell division and form a cell chain;
adjacent cells share cell wall (distinguish them from linear colonies!); maybe unbranched
or branched.
•Coenocytic（多核体） or siphonaceaous forms: one large, multinucleate cell without
cross walls
74
•Parenchymatous and pseudoparenchymatous algae: mostly macroscopic algae with
tissue of undifferentiated cells and growth originating from a meristem with cell division
in three dimensions; pseudoparenchymatous superficially resemble parenchyma but are
composed of appressed filaments
•The reproduction and life history of algae
•1. Asexual Reproduction
•Cellular bisection: many unicellular algae, longitudinal or transverse cell division.
•Zoospores / Aplanospores: Zoospores are flagellated reproductive cells from which a
new individual/colony can grow; sometimes the spores begin to develop within the
mother cell and lack flagella: aplanospores（e.g Chlorella).
•Autospores(似亲孢子）: Nonmotile spores that look like parent cells and cannot
develop into zoospores.
•Autocolony（似亲群体）: In coenobia （定形群体）, each cell goes through several
divisions to form a mini-colony.
•Fragmentation: colonies or filaments break into two to several pieces that continue to
grow.
•Akinetes: Enlarged vegetative cell with thick wall and storage products; survival of
harsh conditions.
•2. Sexual Reproduction
•Gametes look like vegetative cells or very different
•Isogamy: both gametes look identical
•Anisogamy: male and female gametes differ morphologically
•Oogamy: One gamete is motile (male), one is nonmotile (female)
•Monecious（雌性同体）: both gametes produced by the same individual.
•Diecious（雌性异体）: male and female gametes are produced by different individuals.
•Homothallic（同宗配合）: gametes from one individual can fuse (self-fertile).
•Heterothallic（异宗配合）：gametes from one individual cannot fuse (self-sterile).
3.Life history of algae
•Three different types of life cycle, depending on when meiosis occurs, the type of cells
produced, and if there is more than one free-living stage present in the life-cycle
75
•Life-cycle I: major part of life-cycle (vegetative phase) is haploid state, with meiosis
upon germination of the zygote (zygotic meiosis) also referred to as haplontic life cycle,
a single, predominant haploid phase .
•Life-cycle II: vegetative phase is diploid, with meiosis upon formation of gametes
(gametic meiosis) ,also referred to as diplontic life cycle, a single, predominant diploid
phase
•Life-cycle III: three multicellular phases, the gametophyte and one or more
sporophyte(s)
Gametophyte: typically haploid, produces gametes by mitosis
Sporophyte: typically diploid, produces spores by meiosis.
Isomorphic: sporophyte and gametophyte look alike
Heteromorphic: sporo- and gametophyte look different.
Brown Algae: Phylum Phaeophyta
•Prominent macrophytic algae, in freshwater and an almost entirely group in marine
benthic systems with high diversity (1500 species).
•Most of them live in northern and polar waters(Laminariales), some can live in the
tropics(Sargassum).
•Annual and perennial forms, some up to 15 years old.
•Photosynthetic pigments: Chlorophylls a and c; carotenoids, mainly fucoxanthin which
gives the brown algae their characteristic color .
•Carbohydrate food reserve: Laminarin, mannitol.
•Anti-freeze effect of mannitol and glycerol important for kelps in temperate and polar
regions.
•Cell wall component: Cellulose embedded in matrix of mucilaginous algin;
plasmodesmata in some.
•Flagella: 2; only in reproductive cells; lateral; tinsel forward, whiplash behind.
•Brown algae.(a) Bull kelp (Durvillea antarctica) exposed at low tide off a rocky coast in
New Zealand (Left).
•The tough fronds and large holdfast allow this massive kelp to thrive in cold water
where there is plenty of wave action.
•(b) Detail of the kelp Laminaria, showing holdfasts, stipes, and the bases of several
fronds.
•(c) Rockweed (Fucus vesiculosus) densely covers many rocky shores that are exposed at
low tide. When submerged, the air-filled bladders on the blades carry them up toward the
light. Photosynthetic rates of frequently exposed marine algae are one to seven times as
great in air as in water for those rarely exposed.
76
•(a) The brown algae Sargassum has a complex pattern of organization. Sargassum, like
Fucus, is a member of the order Fucals and has a life cycle like Fucus.
•(b) This is the Sargasso Sea in the western Atlantic Ocean.
It is unusual because it has a lot of seaweed growing in it and floating on the surface.
•The giant kelp, Macrocystis pryifera, is one of twenty species found off the California
coast. One Plant can grow for 6 years to over 100 feet in length. This plant and many
others make up the kelp forest that is inhabited by hundreds of marine animals from
snails to whales. The image here shows the gas-filled bladders that help the plant float in
the water.
•The form of Brown Algae
•Thalli of brown algae may be filaments or complex tissues analogous to land plants.
•1.Branched filaments (e.g Ectocarpus)
•2.Pseudoparenchyma(e.g Leathesia)
• Aggregated filaments produce thalli termed pseudoparenchymatous.
•3.Parenchyma(e.g Laminaria)
• thalli formed by cell division in variuous planes; origin polyphyletic
•Growth of Brown Algae: Meristems
1.Diffuse growth: cell division throughout the thallus.
2.Meristem: localized regions of cell division
a)Single apical cell: growth of a filament of one cell‘s width
b) Apical meristem: several cells that divide in different directions, form mutlilayered
thalli .
3.Intercalary meristem: found in large kelps between stipe and blade to increase length of
thallus.
4.Surface meristem: thickens the thallus (blade).
Reproduction of Brown Algae
•Three types of reproductive cells: meiospores, asexual zoospores, gametes.
•Flagella origin at the side of the cells rather than apically.
•Gametes can be isogamous, anisogamous, oogamous.
•Isogamous gametes: one type of gametes settles very soon onto substrate, the other type
(male) remains swimming longer.
•Phenolic compounds are produced by female gametes to attract male gametes.
•Gametophytes produce gametes in plurilocular gametangia.
•Plurilocular gametangia
The multicellular reproductive structures which was produced by gametophyte of more
primitive brown algae, such as Ectocarpus, which may function as male or female
77
gametangia or produce flagellated haploid gametes that give rise to new gametophytes
(parthenogenetic germination).
•Plurilocular sporangia
the multicellular reproductive structure which were produced by diploid sporophytes to
form diploid zoospores that produce new sporophytes.
•Unilocular sporangia
the unilocular reproductive structure which were produced by diploid sporophytes to
form haploid. zoospores that germinate to produce gametophytes, meiosis firstly takes
place within the unilocular sporangia.
•Ectocarpus, a brown algae that has simple branched filaments. These micrographs of E.
siliculosus shows unilocular sporangia and plurilocular sporangia, which are borne on
sporophytes.
•Ectocarpus occurs in shallow water and estuaries throughout the world.
•Types of sexual reproduction, based on gamete form. (a) Isogamy--the gametes are
equal in size and shape. (b) Anisogamy--one gamete, conventionally termed male, is
smaller than the other. (c) Oogamy--one gamete, usually the larger, is nonmotile and
female.
Life Cycle of Brown Algae
•Life Cycle of Ectocarpus: Alternation of isomorphic generations, Sporophyte and
gemetophyte appear morphologically similar; only the sporophyte carries both pluri- and
unilocular sporangia, the gametophyte carries only plurilocular gametangia.
Life Cycle of Laminaria
•Alternation of heteromorphic generations, sporophye is prominent sea kelp, but
gametophyte is microscopically small; unilocular sporangia occur on the surface of the
sporophyte's blade.
•Laminaria japonica Aresh.( right). This is the famous economic seaweed Haidai (“Sea
Ribbon”) used for food, and in medicine and industry for processing algin, mannitol and
iodine. Now commercially cultivated on large scale; annual production over 200, 000
tons dry weight. Distribution: Huanghai sea and East China Sea coast; Japan, Korea,
Pacific coast of Russia.
• (a, b)The cross section structure of Laminaria sp.’s sporophyte.(c) gametophyte of
Laminaria sp.
•In Fucus, gametangia are formed in specialized hollow chambers known as conceptacles,
which are found in fertile areas called receptacles at the tips of the branches of diploid
78
individuals (lower left). There are two types of gametangia--oogonia and antheridia.
Meiosis is followed immediately by mitosis to give rise to 8 eggs per oogonium and 64
sperm per antheridium. Eventually the eggs and sperm are set free in the water, where
fertilization takes place. Meiosis is gametic, and the zygote grows directly into the new
diploid individual.
•Fucus sp. (vesiculosis & spiralis)
Rockweed
Broad, flattened olive green blades firmly attached to rocks in the middle to lower
intertidal zone. Blades are dichotomously branched with ribless air bladders in
pairs. Blades are often twisted and may grow to 1 m.
•The reproductive structure of Fucus
•Undaria pinnatifida Sur.
•Blades flat, midrib placed at the center of the blade, arising from the stipe, usually
pinnately lobed on both sides of the blade, many black cryptostomata scatter over the
surface of blade.Blade structurally composed of three tissues epidermis, cortex and
medulla.
•Distribution: Liaoning, Shandong provinces; Japan, Korea.
•Two species of Sargassum-Sargassum patens Ag.(left) And Sargassum enerve
Ag.(right).
•Distribution: Fujian, Guangdong Provinces and Hongkong; Japan.
Green algae: Phylum Chlorophyta
•Distribution
found in a variety of habitats- most in freshwater, some in marine, soils, tree trunks, and
in symbiotic associations with lichens, freshwater protozoa, sponges, and
coelenterates(腔肠动物）.
•Diversity of species
at least 17,000species and diverse in structure and life history.
•Morphological types
unicellular forms,colonies, unbranched filaments, branched filaments, macroalgal thalli,
and multinucleate.
•Photosynthetic pigments
Chlorophyll a and b; carotenoids, which resemble plant.
•Carbohydrate food reserve
79
starch inside the plastids (often in pyrenoid), which is unique to chlorophytes; stains
with iodine (best way to identify algae as chlorophytes) .
•Flagella
none or 2 (or more); apical or subapical; equal or unequal; whiplash(some with hairs).
•Cell wall
cellulose, hemicelluloses and pectic substances.
•Plastid forms are diverse, but uniform within one given genus (taxonomic marker).
•Snow algae are unique because of their tolerance to temperature extremes, acidity, high
levels of irradiation, and minimal nutrients for growth. This picture shows snow algae
produces ‘red snow’ on Alaska glaciers.
•Dormant zygote of the snow alga Chlamydomonas nivalis
•This is most well-known snow alga. Bloom of this alga causes visible red snow
(watermelon snow). This species is common in North America, Japan, Arctic, Patagonia.
The algae prefer snow surface rather than ice on glaciers. The pictures above are different
life stage of the alga.
•Chlorophyceae，which consists of mainly fresh water species
•Chlamydomonas is an example of a motile unicellular Chlorophyceae
•The common freshwater green alga with a unicellular form and two equal flagella.
• Cuplike chloroplast, very common; 500 species in the genus.
•Be widely used as a model system for molecular studies and other cell process.
•A Polyphyletic group-consists of several distinct lineages, all of which coincidentally
are unicellular with two equal flagella.
•Reproduction
•1.asexual reproduction: the haploid nucleus usually divides by mitosis to produce up to
16 daughter cells within the parent cell wall, each cell secrete a wall around itself and
develops flagella.
•2. sexual reproduction: involving the fusion of gametes, which resemble the vegetative
cells.
• The microstructure of Chlamydomonas.
•The ultrastructure of Chlamydomonas, a unicellular green alga.
•Life cycle of Chlamydomonas.Sexual reproduction occurs when gametes of different
mating types come together, cohering at first by their flagellar membrances and then by a
slender protoplasmic thread-the conjugation tube.
•Volvox is the most spectacular of the motile colonial Chlorophyceae
80
•Colonies of various shapes and sizes of aggregated and flagellated cells resembling
Chlamydomonas with haploid.
•Hollow spheroid, which are made up of a single layer of 500 to 60,000 vegetative,
biflagellated cells.
•In the process of asexual reproduction, daughter colony must turn inside out before it
can become motile.
•Sexual reproduction-always oogamous which is induced by a glycoprotein produced by
male colony.
•Several colonial Chlorophyceae. Gonium (盘藻属） forms a flattened colony of 4 - 32
cells. Since the genus is coenobic, each colony of the same species of Gonium has the
same number of cells. Also, if one or more cells of the colony die they will not be
replaced.
•Pandorina （实球藻属）
•Eudorina （空球藻属）. In these algae, cells similar to those of Chlamydomonas
adhere in a gelatinous matrix to form multicellular colonies propelled by the beating of
the flagella of the individual cells. Varying degree of cellular specialization are found in
diffenent genera.
•Volvox sp is thought to represent the culmination of the order. Apparently there is no
further specialization of the group and it did not lead to any other advanced algal form.
•Note the large number of cells forming the hollow sphere.
•Volvox reproduces asexually by the formation of daughter colonies.
Several cells in the
parent colony termed gonidia differentiate into reproductive cells. Generally the gonidia
divide forming a minute miniature of the parent colony within the hollow parental sphere.
These daughter colonies eventually are released through the rupture of the parent colony.
•Sexual reproduction in Volvox begins in the same way as asexual reproduction.
•The gonidia, instead of becoming daughter colonies, either become eggs or sperm
`packets' so the reproduction is oogamous.
•The species may be monoecious or dioecious.
•Finally, the zygote divides meiotically ultimately producing a single motile zoospore.
This cell swims for a short period then divides successively to form a small colony.
•Mature Volvox sp. zygotes
•Volvox sp.Sexual Reproduction
•(a) Gonidia developing into female eggs
•(b) Volvox sp. sperm packets
•The class Chlorophyceae also include nonmotile unicellular members
•Chlorococcum （绿球藻属）. At the upper right is filled with asexual zoospore, which
have formed mitotically within the cell.The smaller cells in the lower left are biflagellate
zoospores. The nonmotile vegetative cell is at lower left.
•Some Chlorophyceae are nonmotile colonies
81
•(a) ‘Water net’ hydrodictyon （水网藻属）, a colonial member of the Chlorophyceae.
•(b) A high magnification of a portion of Hydrodictyon reticulatum.
•There are also filamentous and parenchymatous Chlorophyceae
•Oedogonium, an unbranched filamentous member of the Chlorophyceae. A section of
vegetative filament showing annular star.
•Sexual reproduction in Oedogonium is oogamous. Each oogonium produces a single
egg, whereas each antheridium produces two multiflagellated sperm.
•(a) shows egg, (b) shows a zygote
•Class Ulvophyceae, the Ulvophytes, consists of maily marine species
•Ulvophytes: filamentous, flat sheets of cells, or macroscopic and multinucleate.
•Closed mitosis in which the nuclear envelope persists and the spindle is persistent
through cytokinesis.
•The flagellated cells have two, four, or many apical,forward-directed flagella.
•Life cycle: an alternation of isomorphic generations(marine species), or not (freshwater
species).
•Cladophora （刚毛藻属）, a member of the class Ulvophyceae, is widespread in
marine and freshwater habitats.The above picture shows its branch filaments and habitat
in a stream in California.
•Sea lettuce, Ulva, a common member of the class Ulvophyceae that grows on rocks,
and similar places in shallow sea worldwide
•Life cycle of Ulva
•In the sea lettuce, Ulva, we can see the reproductive pattern known as an alternation of
generations, in which one generation produces spores (left), the other gametes (right).
The haploid (n) gametophyte produces haploid isogametes, and the gametes fuse to form
a diploid (2n) zygote. A sporophyte, a multicellular body in which all the cells are diploid,
develops from the zygote. The sporophyte produces haploid spores by meiosis. The
haploid spores develop into haploid gametophytes, and the cycle begins again.
The siphonous marine, characterized by very large, branched,coenocytic cells that
are rarely septate in Ulvophyceae
•Four genera of siphonous green algae of the class Ulvophyceae. (a) a species of Codium
（松藻属）, abundant along the Atlantic coast. (b) Ventricaria(Valonia)（法囊藻属）,
common in tropical waters; individuals are often about the size of a hen’s egg.
•(c) Acetabularia, which has been widely used in experiments on the genetic basis of
differentiation. The siphonous green algae are primarily diploid. The gametes are the only
haploid cells in life cycle.
•(d) Halimeda, siphonous green alga that is often dominant in reefs in warmer waters
throughout the world.
82
Class Charophyceae, the Charophytes, includes members that closely resemble
plants
•The form of algae
unicell, colony, filament, and parenchyma
•Asymmetrical flagellated cell, some of which have distinctive multilayered structure.
•Breakdown of the nuclear envolope at mitosis, persistent spindles or phragmoplasts at
cytokinesis,and the presence of phytochrome.
•Conjugation in Spirogyra, this images show how Spirogyra conjugates, a form of sexual
reproduction. Spirogyra and its relatives can be found during summer as pond scum,
floating mats in ponds.
•Two filaments of Spirogyra form conjugation tubes. The contents of one cell passes
through the tube and fuses with a cell from the other filament.
•Fertilization occurs and a zygote is formed. This develops into a thick walled resistant
zygospore. These zygospores can withstand harsh conditions. They can survive the cold
winter or when a pond dries up.
•It may take a long time before new filaments start to grow. Here the start of the
development into new filaments is visible as the spiral chloropasts are beginning to show.
Charales have plantlike characteristics
•(a) Chara, a stonewort(class Charophyceae) that grows in shallow waters of temperate
lakes.(b) Chara showing gametangia.The top structure is an oogonium, and that below is
an antheridium.
Red Algae: Phylum Rhodophyta
•Main Characteristics
•Number of Species
4000-6000
•Structure
the vast majority of red algae are more structurally complex, macroscopic seaweeds
3. Photosynthetic pigments
Chlorophyll a and d; phycobilins (phycocyanin and phycoerythrin) which give red
algae their distinctive color; carotenoids; pyrenoids(primitive)
4. Carbohydrate food reserve
Floridean starch(like glycogen)
5. Flagella
None
6.Cell wall component
Cellulose microfibrils embedded in matrix(usually galactans)(半乳糖）; deposits of
calcium carbonate in many.
7.Habitat
Predominatly marine, about 100 freshwater species;many tropical species.
Extreme environment： deepest photosynthetic organism is a coralline alga at 210 m
depth; unicellular red algae grow in acidic hot springs .
83
Pit connection in the red algae
•A pit connection in the red alga Palmaria. Pit connection are distinct, lens-shaped plugs
that form between the cells of red algae as the cells divide. These connections are also
formed frequently between the cells of adjacent filaments that come into contact with
each other, linking together the bodies of red algae. Pit-connection cores are protein, and
their out cap layers are, at least in part,polysaccharide.
•Marine red algae.(a) In Bonnemaisonia hamifera, the basically filamentous structure of
the red algae is clearly evident.the branched filaments of this red alga are
hooked,enabling it to cling to other seaweeds.(b) Jointed coralline algae in a tidal pool in
California.(c) The reef-stabilizing, crustose coralline red alga Porolithon craspedium.(d)
Irish moss (Chondrus crispus),an important souce of carrageenan
Sexual Reproduction in Red Algae
•Oogamy occurs in all red algae
•Carpogonium: larger, non-flagellate female gamete produced on female gametophyte.
•Carpogonia are produced at the tip of special branches (carpogonial branches); typically
flask-shaped with long, thin neck called trichogyne.
•Spermatium: non-flagellate male gamete produced in spermatangium on male
gametophyte; spermatia move passively (currents) to carpogonia.
•Fertilization: spermatium fused with tip of trichogyne; a channel is enzymatically
opened to allow the spermatium‘s nucleus to enter.
•Carpospores: several diploid spores produced by mitosis of the zygote on the diploid
carposporophyte.
Red algae have complicated life histories
•Biphasic life cycle occurs in evolutionary early species
•Triphasic life cycle is unique to evolutionary young red algae, which occurs in most red
algae and consists of three phases:
1).a haploid gametophyte; 2).a diploid phase, called a carposporophyte;and 3).another
diploid phase, called tetrasporophyte
•Life cycles can change in some species, e.g. Porphyra: monospore, aplanospores,
gametophyte (sexual reproduction).
Life cycle of Porphyra
•Porphyra umbilicalis"Nori"
This sheet forming Rhodophyte feels very soft and slippery. It stretches slightly and looks
almost like pink cellophane, although color, size, and shape can be extremely variable.
Common in spring and summer attached to rocks or other algae, as seen here as an
84
epiphyte on Fucus.
This image shows the nets where Porphyra is grown.
•Powdered agar called agar-agar is commonly sold in Asian food stores. The name "agaragar" is of Malay origin and means "jelly." Agar-agar is used as a thickening agent in
foods much like gelatin is used. Most agars come from the Rhodopyta, including the
genera Gelidium, and Gracilaria.
•Left: The dried blade of Porphyra perforata, a membranous red alga from the rocky
intertidal zone of southern California. In Japan, species of Porphyra called "nori" are
cultivated for food. Right: Crackers wrapped in nori and package of nori sheets used for
wrapping sushi.
•The red alga Gelidium pulchrum from the intertidal zone of San Diego County,
California. Gelidium is one of the red alga species harvested for the polysaccharide gum
called agar (agar-agar). A larger species (Gelidium cartilagineum) from deeper waters
was extensively harvested by divers along the southern California coast during World
War II when Japanese agar supplies were cut off. Gelidium for agar manufacture is now
collected extensively in California.
•Polysiphonia sp. and its sexual reproductive structure
•Life cycle of Polysiphonia sp.
85
Chapter 11 Fungi
This chapter will deal with the following topics:
•
•
•
•
•
•
The Role of Fungi
Biology and Characteristics of Fungi
Phylum Zygomycota
Phylum Ascomycota
Phylum Basidiomycota
Symbiotic Relationships of Fungi
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. In what ways do the fungi differ from all other life form? In other words,
what are the distinctive characteristics of the fungi?
2. From what type of organism is it thought that fungi evolved?
3. What are the distinguished characteristics of Chytridiomycota, Zygomycota,
Ascomycota, and Basidiomycota?
4. What is a yeast, and what is the relationaship of yeasts to the other groups of
fungi?
5. What kinds of symbiotic relationships exist between fungi and other
organism?
What are fungi?
•Eukaryotic, spore-bearing, heterotrophic organisms that produce extracellular enzymes
and absorb their nutrition.
The Role of Fungi
•Over 70,000 species of fungi have been identified, with some 1700 new species
discovered each year.
•Fungi are important ecologically as decomposers, which play an important role in
carbon and nitrogen recycle in biosphere. On average, the top 20 centimeters of fertile
soil contains nearly 5 metric tons of fungi and bacteria per hectare.
•Fungi are important medically and economically as pest, pathogens, and producers of
certain chemicals.
•Fungi form important symbiotic relationships.
Major Characteristics of Fungal Phyla
•Chytridiomycota(790 species)
•Representatives: Allomyces, Coelomomyces
•Nature of Hyphae: aseptate, coenocytic
86
•Method of Asexual Reproduction: Zoospores
•Type of Sexual Spore: None
•Common Plant Diseases: brown spot of corn, crown wart of alfalfa, black wart of potato.
•
Zygomycota (1060 species)
•Representatives: Rhizopus (common bread mold)
•Nature of Hyphae: aseptate, coenocytic
•Method of Asexual Reproduction: Nonmotile spores
•Type of Sexual Spore: Zygospore(in zygosporangium)
•Common Plant Diseases: Soft rot of various plant part.
• Ascomycota (32,300 species)
•Representatives: Powdery mildews, Morchella(羊肚菌） (edible morels), Tuber
(truffles)
•Nature of Hyphae: septate
•Method of Asexual Reproduction: Budding, conidia(nonmotile spores)(分生孢子）,
fragmentation.
•Type of Sexual Spore: Ascospore（子囊孢子）
•Common Plant Diseases: powdery mildew, brown rot of stone fruits, chestnut blight,
Dutch elm disease.
•Basidiomycota (22,244 species)
•Representatives: Mushrooms (Amanita, poisonous; Agaricus, edible), stinkhorns,
puffballs, shelf fungi, rusts, smuts
•Nature of Hyphae: Septate with dolipore
•Method of Asexual Reproduction: Budding, conidia(nonmotile spores, including
urediniospores 锈孢子), fragmentation
•Type of Sexual Spore: Basidiospore（担孢子）
•Common Plant Diseases: Black stem rust of wheat and other cereals, white pine blister
rust, common corn smut, loose smut of oats, Armillaria root rot
•
Fungi.(a) The chytrid Polyphagus euglenae parasitizing a Euglena cell.The cytoplasm
of the rounded-up Euglena cell is degraded. (b)A flower fly (syrphus) that has been
killed by the fungus Entomophthora muscae, a zygomycete. (c) A common morel
（龙葵）, Morchella esculenta(羊肚菌）, ascomycete.The morels are among the
most prized of the edible fungi.(d) A mushroom,Hygrocybe aurantiosplendens, a
87
species of Basidiomycetes. A mushroom is made up of densely packed hyphae,
collectively known as the mycelium.
Biology and Characteristics of Fungi
1.Most fungi are composed of hyphae
Hyphae:fungal filament.
Mycellium: Hyphae form a mass of strands called a mycelium.
Septate: the hyphae of most species of fungi, which are divided by partitions or
crosswalls.
Aseptate: hyphae lacking septa.
Coenocytic: multinucleate.
•Cell walls are made of chitin, a nitrogen containing polysaccharide, which is the same
material found in the hard shells, or exoskeletons, of arthropods（节肢动物）.
The image shows fungal hyphae ( Septated_hyphae). These hyphae can grow
extremely rapidly. In 24 hours, 0.6 miles of hyphae can be produced.
2. Fungi are heterotrophic absorbers
•Fungi cannot produce their own food. Such organisms are called heterotrophs, which
can be divided into several categories:
1) Saprobe(saprophyte)（腐生）: Heterotroph that derives its food from non-living
organic carbon sources.
2) Parasite（寄生）: Heterotroph that derives its food from the living cells of another
organism referred to as the host
3) Facultative Parasite（兼性寄生）: Heterotroph that is primarily a saprobe, but when
opportunity presents itself, can be a parasite.
4) Facultative Saprobe（兼性腐生）: Heterotroph that is primarily a parasite, but when
opportunity presents itself, can become a saprobe.
5) Symbiont (used here in the mutualistic sense): Heterotroph that derives its food from
another living organism, but the relationship is mutually beneficial to both organisms
involved, e.g. lichens = fungus and alga.
•
Specialized hyphae-rhizoids and haustorium
3.Fungi have unique variations of mitosis and meiosis
•All fungi lack centrioles, but they form unique structures called spindle pole bodies,
which appear at the spindle poles
4.Reproduction of Fungi
• Fungi reproduce via spores (nonmotile reproductive cells dispersed by wind or by
animals), both sexually and asexually. Spores are borne on fruiting bodies which are
composed of aerial hyphae. Sometimes these bodies form complex structures like the
classic mushrooms that you see.
88
• Fungi can produce spores either sexually or asexually.
•Fungal cells are haploid. But in sexual reproduction for some, different mating strains
fuse together, while the nuclei still remain separate in the cytoplasm.
•Hyphae that contain two genetically distinct nuclei within each cell are called
dikaryotic (n + n); while those that have only one are monokaryotic (n).
•When they are ready to undergo sexual reproduction, the nuclei will fuse and then
undergo meiosis to produce haploid spores.
Phylum Zygomycota
· About 1060 sp of bread molds; they are typically the molds that you see develop on
foods in your refrigerator.
· Hyphae are coenocytic.
· Asexual reproduction: the hyphae produce fruiting bodies called sporangia (spore
sacs). Each one through mitosis produces asexual spores.
•Sexual reproduction: Occurs when hyphae of different mating types come
together. They grow together, produce a gametangium which later fuse to make a
diploid nucleus.
•This new cell will then become zygospore which can wait out harsh conditions. Just
before germinating the diploid zygospore will undergo meiosis and then produce a
sporangium. The sporangium will then produce spores via mitosis. Note that the
zygospore is the only diploid structure in zygomycetes.
Rhizopus stolonifer
•Rhizopus stolonifera (Bread Mold)（匍枝根霉）
•This species is one of the most common members of this division. This organism causes
the black bread mold that forms cottony masses on the surface of moist bread exposed to
the air. This picture shows Rhizopus stolonifer rot on harvested peaches.
•Sporangia form on the tips of sporangiophores, which are erect branches formed directly
above the rhizoids. Each sporangium begins as a swelling into which a number of nuclei
flow, and it is eventually cut off from the sporangiophores by the formation of a
septum.This picture shows Rhizopus stolonifer sporangium and sporangiophore. Note
rhizoids stolons and hyphae.
•Sexual reproduction occurs only between different mating strains, which have been
traditionally labelled + and – types(heterothallic). When the two strains are in close
proximity, hormones are produced that cause their hyphal tips to come together and
develop into gametangia, which become separated from the rest of the fungal body by the
formation of septa.
Life Cycle of Rhizopus stolonifer
89
Phylum Ascomycota
•1. Ascomycetes are distinguished by the presence of Saclike Compartments where
Sexual Production of Spores Form.
•2. This Phylum includes the unicellular yeast, cup fungi, truffles, morel and mildews
that are destructive parasites of food crops.
•3. Sac Fungi can reproduce both Sexually and Asexually(Conidia).
•4. SAC FUNGI REPRODUCE ASEXUALLY BY FORMING SPORES AT THE TIPS
OF THEIR HYPHAE.
•SAC FUNGI REPRODUCE SEXUALLY BY FORMING AN ASCUS (ASCI) - A
SAC STRUCTURE IN WHICH SPORES ARE FORMED.
•6. Sexual reproduction involves the formation of a characteristic cell-the ascus-in
which meiosis takes place and within which ascospores are formed;
•7. The Female gametangia is called an ASCOGONIUM . The Male Gametangia is
called an ANTHERIDIUM.
• 8. As the Ascogonium and Antheridium approach one another, a tube forms between
them and the nuclei from the Antheridium cross and enters the Ascogonium.
•9. The Parent Fungi form a visible Cup-like Sexual Reproductive structure called the
Ascocarp.
10. Within the Ascocarp, the Sacs called Asci develop at the tips of the Hyphae and Form
ASCOSPORES, which are released.
11. Brewer's and Baker's YEAST are Unicellular Sac Fungi that can Reproduce
Sexually by forming Asci.
•There are about 32,300 species of ascomycetes.
•Aspergillus conidiophores
Conidia are grown on elaborate structures called
conidiophores. These are usually stalked, lifting the conidia off the substrate for better
dispersal .They often produce hundreds or thousands of conidia at a time.
Ascocarp(ascomata)(子囊果）
•Both asci and ascospores are unique structures that distinguish the ascomycetes from all
other fungi.
•Ascus formation usually occurs within a complex structure composed of tightly
interwoven hyphae, which is called Ascocarp, many of them are macroscopic.
•The asci usually develop on the inner surface of the ascoma, which is usually called the
hymenium,or hymenial layer.
Ascocarp can be divided into 3 types:
1. Apothecium（子囊盘）: open and more or less cup-shaped.
90
2.Cleistothecium（闭囊壳）: closed and spherical.
3.Perithecium（子囊壳）: spherical to flask-shaped with a small pore through which
the ascospores escape.
•Mature perithecium in a stomatal chamber of Asteroxylon(left). This shows the two
layers of the wall (w) and the opening through which the ascospores are released (n).
(scale bar = 100µm)
•The typical life cycle of ascomycete
Phylum Basidiomycota
•About 22,300 , which includes the mushrooms, toadstools(羊肚菌）, stinkhorns（鬼
笔）, puffballs（马勃）, and shelf fungi, as well as rusts and smuts.
•The Basidiomycota are distinguished from other fungi by their production of
basidiospores, which are borne outside a club-shaped spore-producing structure called
basidium.
•The mycelium is always septate, and the septa are perforated.
•Mycelium passes through two distinct phases-monokaryotic (primary mycelium)
and dikaryotic (secondary mycelium).
•The apical cells of the diakaryotic mycelium usually divide by the formation of
clamp connections, which ensure the allocation of one nucleus of each type to the
daughter cells.
•The mycelium that forms the basidiomata is called the tertiary mycelium.
•Classification of Basidiomycota:
Basidiomycetes
Teliomycetes(the rusts)
Ustomycetes (the smuts)
•An elaborate septal pore structure, the dolipore septum, is characteristic of the
mycelium of most basidiomycetes.
•Life
cycle of a mushroom (phylum Basidiomycota, a hymenomycete). Monokaryotic,
primary mycelia are produced from basidiospores and give rise to dikaryotic,
secondary mycelia, often following the fusion of different mating types, in which
case the mycelia are heterokaryotic. Dikaryotic, tertiary mycelia form the basidioma,
within which basidia form on the hymenia that line the gills, ultimately releasing up
to billions of basidiospores.
91
Life cycle of a mushroom
•Scanning electron micrographs of basidiospores of the inky cap mushroom, Coprinus
cinereus (鬼伞）. (a) The hymenium showing numerous basidia frozen at the time of
basidiospore release.(b) The top of a basisium, with basidiospores, each attached to a
stalklike sterigma.
•Clamp connections. (a) In the Basidiomycetes, dikaryotic hyphae characteristically are
distinguished by the formation of clamp connections during cell division in tips of
hyphae. They presumably ensure the proper distribution of the two genetically distinct
types of nuclei in the basidioma. Two septa form to divide the parent cell into two
daughter cells.
•Stained section through the gills of Coprinus (鬼伞）, a common mushroom, at
progressively higher magnifications. The hymenial layer is stained darker in each of these
preparations.(a) Outlines of the gills.(b) gills and hymenial layer.(c) developing basidium
and basidiospores.(d)mature basidiospores.
92
Chapter 12 Bryophytes
In this chapter we’ll deal with the following topics:
•Distribution and habitat
•The Relationships of Bryophytes to Other Groups
•Comparative Structure and Reproduction of Bryophytes
•Liverworts: Phylum Hepatophyta
•Hornworts: Phylum Anthocerophyta
•Mosses: Phylum Bryophyta
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What are the general characteristics of the bryophytes? In other words, what
does it take to be a bryophytes?
2. What are the three phyla of bryophytes? How are they similar to and
different from one another?
3. How does sexual reproduction occur in bryophytes? What are the principal
parts of the resulting sporophyte of most bryophytes?
4. How can the three types of liverworts be distinguished from one another?
5. What are the distinguished features of the hornworts?
6. What are the distinguishing features of each of the three classes of mosses?
1.Distribution and habitat of Bryophyte
•Distribution
•They are found in many different habitats including tundra, desert and tropical forests
• Most live in damp environments because water is needed for the sperm to travel to the
egg cells in fertilization
• Sphagnopsida (“Peat Mosses”)
Sphagnum moss(泥炭藓） is said to occupy 1% of the world's surface (about 1/2 the
size of the U.S.) .
•Andreaeopsida
("Lantern Mosses")
* Most species prefer to live in cool-temperate to polar regions
*most are found in the Southern Hemisphere
*they are also found at high altitudes in sunny alpine regions and even in the tropics,
but still others grow in damp areas
• Polytrichopsida ("Nematodontous Mosses")
* Found in coniferous forests at many different elevations
93
2.Habitat
•Bryophytes are found in damp environments
* they are able to absorb water through most of their bodies and therefore use the water
from the environment for reproduction and other life processes
* They are able to move water throughout their bodies by diffusion, capillary action
and cytoplasmic streaming
•Many are found growing on exposed rock surfaces
* they use their rhizoids which hook into tiny cracks and help to anchor the plants
* the rest of the moss leaf is a single layer of cells so that all the cells are very close
to the environment in which they live.
•Mosses cover the
roots of a rainforest tree
•Moss-covered carving in Bali
•The Relationships of Bryophytes to Other Groups
•Bryophytes and vascular plants share a number of characters that distinguish them from
the charophytes.
•The presence of male and female gametangia, called antheridia and archegonia,
respectively, with a protective layer called a sterile jacket layer;
•Retention of both the zygote and the developing multicellular embryo, or young
sporophyte, within the archegonium or the female gametophyte;
•3. The presence of a multicellular diploid sporophyte, which results in an increased
number of meioses and an amplification of the number of spores that can be produced
following each fertilization event;
•4. Multicellular sporangia consisting of a sterile jacket layer and internal sporeproducing (sporogenous) tissues;
•5. Spores with walls containing sporopollenin, which resists decay and drying;
•6.Charophytes lack all of these characters;
•
•7.Living bryophytes lack the water- and food-conducting (vascular) tissues-xylem and
phloem;
•8. Life cycle of bryophytes exhibit alternating heteromorphic gametophytic and
sporophytic generations- the gametophyte is dominant and free-living and the sporophyte
is small, permanently attached to its parental gametophyte;
•9. The bryophyte sporophyte is unbranched and bears only a single sporangium,
whereas the sporophytes of vascular plants are branched and bear many more sporangia.
94
•Gametangia of Marchantia(地钱）, a liverwort. (a) a developing antheridium,
consisting of a stalk and sterile-that is , non-sperm-forming-jacket layer enclosing
spermatogenous tissue. The spermatogenous tissue develops into spermatogenous cells,
each of which forms a single sperm propelled by two flagella.
•（b) Several archegonia at different stages of development. An egg is contained in the
venter, a swollen portion at the base of each flask-shaped archegonium. When the egg is
mature, the neck canal cells disintegrate, creating a fluid-filled tube through which the
biflagellated sperm swim to the egg in response to chemical attractants. In Marchantia,
the archegonia and antheridia are borne on different gametophytes.
•A cladogram showing some of the character traits shared by the green algae and the
major groups of plants. The term "embryophyte," a synonym for plant, refers to the fact
that a multicellular embryo is retained within the female gametophyte. This cladogram
reflects one point of view that mosses share a more recent common ancestor with the
vascular plants than do the liverworts or hornworts.
•Mosses: Phylum Bryophyta
•Main Characteristics of Bryophyta (Mosses)
•Number of species: 9500
•General Characteristics of Gametophyte
•Dominant and free-living generation;
•Leafy;
•Multicellular rhizoids;
•Most cells have numerous chloroplasts;
•Many produce gemmae（胞芽）;
•Protonema stage that grows by marginal meristem followed by further growth from an
apical meristem in Sphagnum(泥炭藓属）;
•Growth by apical meristem only in Bryidae（真藓纲）;
•Some species have leptoids（类韧皮细胞） and nonlignified hydroids（水螅状导水
细胞）,which are specilized tissues for water and food conduction.
•3. General Characteristics of Sporophyte
•Small and Nutritionally dependent on gametophyte;
•Unbranched;
•Consists of foot, long seta, and sporangium in Bryidae;
•Phenolic materials in epidermal cell walls;
•Stomota;
•Some species have leptoids and nonlignified hydroids.
95
4. Habitats
•Mostly moist temperate and tropical;
•Some Arctic and Antarctic;
•Many in dry habitats;
•A few aquatic
•A “true moss.” Protonema of a moss with a budlike structure, from which the leafy
gametophyte will develop. Protonemata are the first stage of the gametophyte generation
of mosses and some liverworts. They often resemble filamentous green algae.
•Protonema of Mosses
Conducting strands in the seta, or stalk, of a sporophyte of the moss Dawsonia
superba
•(a) General organization of the seta as seen in transverse section with the scanning
electron microscope.
•(b) Transverse section showing the central column of water-conducting hydroids
surrounded by a sheath of food-conducting leptoids and the parenchyma of the cortex.
•(c) Longitudinal section of a portion of the central strand, showing hydroids, leptoids,
and parenchyma
•Gametangia of Mnium（提灯藓属）, a unisexual moss.
•(a) Longitudinal section through an archegonial head showing the pink-stanied
archegonia surrounded by sterile structures called paraphyses.
•(b) longitudinal section through an antheridial head showing antheridia surrounded by
paraphyses.
•Female gametophyte
•2. Male gametophyte
•3 & 4. Female gametophytes with young sporophytes
•5. Female gametophyte with mature sporophyte
•6. Sporophyte with attached calyptra
•7. Sporophyte
•8. Calyptra
•The moss gametophyte and sporophyte
•A moss plant consists of leaves on a stem. While there are many cells in a moss leaf, in
most cases the cells are in one plane so that the leaf is only one cell thick. This is
96
markedly different to the leaves of vascular plants which are many cells thick. Mosses
produce spores in capsules that often grow on short stalks. This picture shows the trailing
moss Papillaria flavolimbata can form extensive curtains of strands.
•The silvery-green moss Bryum argenteum（真藓） is a widespread species which
occurs from forest to town.
•These rosettes of red leaves are the tips of the male plants of the moss Polytrichum
juniperinum（金发藓）.
•Spore capsules of the moss Funaria hygrometrica（葫芦藓）. The green capsules
contain immature spores and the brown capsules contain mature spores.
•Bryum argenteum（真藓）, a moss with more densely packed stems and shorter,
overlapping leaves.
•A clump of a moss in the genus Bryum, showing the nodding spore capsules common in
this genus.
•Polytrichum commune one of the larger mosses with mature sporophytes
Hornworts
•Hornworts have neither leaves nor stems. They grow as flat, green lobes called a
thallose growth form.
•A fertile hornwort produces its spores in a long, tapering horn-like capsule that grows up
from the lobes. The whole horn-like structure is the capsule and there is no stalk.
•A hornwort in the genus Phaeoceros showing the thallose growth form and a few
immature green spore capsules.
Liverworts
•There are two types of liverworts — leafy and thallose.
•The leafy liverworts have leaves on stems and look rather like mosses.
•Thallose liverworts grow as flat green lobes and some of these liverworts look like
hornworts.
•Lethocolea squamata, a leafy liverwort which grows on the ground, in habitats ranging
from wet sclerophyll forests to hot dry mallee areas. Occasionally it even grows as a
floating aquatic plant.
•The lobes of a thallose liverwort in the genus Marchantia.
97
•The stubby Y-shaped lobes of a thallose liverwort in the genus Riccia.
98
Chapter 13 Seedless Vascular Plants
In this chapter we’ll deal with the following topics:
•
•
•
•
•
•
Evolution of Vascular Plants
Organization of the Vascular Plant Body
Reproductive Systems
The Phyla of Seedless Vascular Plants
Phylum Lycophyta
Phylum Pterophyta
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What explanations are there for the evolutionary origin of microphylls and
megaphylls? Which groups of seedless vascular plants have microphylls?
Which have megaphylls?
2. What is meant by homospory and heterospory? What are the relative sizes of
the gametophytes produced by homosporous and heterosporous produced by
homosporous and heterosporous plants?
3. What are the characteristics of Phylum Pterophyta?
4. In terms of their structure and mothod of development, how do eusporangia
differ from leptosporangia? Which ferns are eusporangiate? Which are
leptosporangiate?
Evolution of Vascular Plants
•By the Early Devonian, some 408 to 387 million years ago, small leafless plants with
simple vascular systems were growing upright on land. It is thought that their pioneering
ancestors were bryophyte-like plants, seen here near the water at the center, that invaded
land sometime in the Ordovician (510 to 439 million years ago).
•The vascular
colonizers shown are, from left to center, very tiny Cooksonia with
rounded sporangia, Zosterophyllum with clustered sporangia, and Aglaophyton with
solitary, elongated sporangia. During the Middle Devonian (387 to 374 million years ago),
larger plants with more complex features became established. Seen here on the right are,
from back to front, Psilophyton(裸蕨）, a robust trimerophyte with plentiful sterile and
fertile branchlets, and two lycophytes with simple microphyllous leaves, Drepanophycus
and Protolepidodendron.
•A fossil of Cooksonia, one of the earliest and simplest plants known, from the Late
Silurian period(414-408 million years ago).
99
•Cooksonia consisted of little more than a branched stem with terminal sporangia, or
spore-producing structures.
Organization of the Vascular Plant Body
•A diagram of a young sporophyte of the club moss Lycopodium lagopus(石松）, which
is still attached to its subterranean gametophyte. The dermal, vascular, and ground tissues
are shown in transverse sections of (a) leaf, (b) stem, and (c) root. In all three organs, the
dermal tissue system is represented by the epidermis, and the vascular tissue system,
consisting of xylem and phloem, is embedded in the ground tissue system.
•The ground tissue in the leaf--in Lycopodium, a microphyll--is represented by the
mesophyll, and in the stem and root by the cortex, which surrounds a solid strand of
vascular tissue, or protostele. The leaf is specialized for photosynthesis, the stem for
support of the leaves and for conduction, and the root for absorption and anchorage.
•Tracheary elements, the conducting cells of the xylem. A portion of the stem of
Dutchman‘s pipe (Aristolochia)（马兜铃属） in (a) transverse and (b) longitudinal
views, showing some of the distinctive types of wall thickenings exhibited by tracheary
elements. Here, the wall thickenings vary, left to right, from those elements formed
earliest in the development of the plant to those formed more recently.
•Steles. (a) A protostele, with diverging traces of appendages (leaves or leaf precursors),
the evolutionary precursors of leaves. (b) A siphonostele with no leaf gaps; the vascular
traces leading to the leaves simply diverge from the solid cylinder. This sort of
siphonostele is found in Selaginella（卷柏）, among other plants. (c) A siphonostele
with leaf gaps, commonly found in ferns. (d) A eustele, found in almost all seed plants.
Siphonosteles and eusteles appear to have evolved independently from protosteles.
•Microphylls and megaphylls. Longitudinal and transverse sections through (a) a stem
with a protostele and a microphyll and (b) a stem with a siphonostele and a megaphyll,
emphasizing the nodes, or regions where the leaves are attached. Note the presence of
pith and a leaf gap in the stem with a siphonostele and their absence in the stem with a
protostele. Microphylls are characteristic of lycophytes, while megaphylls are found in all
other vascular plants.
•Evolution of microphylls and megaphylls. (a) According to one widely accepted theory,
microphylls evolved as outgrowths, called enations, of the main axis of the plant. (b)
Megaphylls evolved by fusion of branch systems.
•Reproductive Systems
•Homosporous plants produce only one kind of spore, whereas heterosporous plants
produce two types
•Early vascular plants produced only one kind of spore as a result of meiosis; such
vascular plants are said to be homosporous.
100
•Heterospory-the production of two types of spores in two different kinds of sporangiais found in some of the lycophytes, in a few ferns, and in all seed plants.
•The two types of spores are called microspores and megaspores, which are produced in
microsporangia and megasporangia respectively.
•Microspores give rise to male gametophytes(microgametophytes), and megaspores
give rise to female gametophytes (megagametophytes)
•Generalized life cycle of a vascular plant, in which the sporophyte is the dominant phase
of the life cycle.
•Fern Life Cycle.Ferns belong to the Division Pterophyta characterized by vascular
plants with leaves (fronds) arising from subterranean, creeping rhizomes. The dominant
(conspicuous) part of the life cycle is the diploid, leaf-bearing sporophyte.
•Phylum Lycophyta
•Some are more or less dichotomous
•Sporophyte differentiated into roots , stems, and leaves.
•Some are homosporous (Lycopodiaceae), and the others are heterosporous
(Selaginellaceae).
•Type of leaves: microphyll.
•Type of stele: most with protostele or modified protostele.
•Sporangia: on or in the axils of sporophylls.
•Lycopodium lagopus（石松）
Selaginella
•Leafy herbs with dichotomously branched stems. Roots borne on wiry rhizophore
arising from forks in stems. Leaves alternate, opposite or whorled, simple, one-veined,
sometimes dimorphic (two sizes), with scale-like ligule (early deciduous).
•Sporangia borne in axils of fertile leaves (sporophylls). Plants heterosporous.
Microsporangia and megasporangia borne in the same or different strobili. Microspores
small, numerous. Megaspores large, 4 per megasporangium.
•Image of young sporophyte developing from megaspore
•The life cycle of Selaginella, which is heterosporous
•Phylum Pterophyta
•About 11,000 species
101
•No dichotomously branched.
•Differentiated into roots, stems, and leaves.
•All homosporous except for Marsileales （萍目） and Saviniales , which are
heterosporous.
•Type of leaves: megaphyll.
•Type of stele: protostele in some; siphonostele or more complex types in others.
•Sporangia: on sporophylls; some clustered in sori.
•Ferns possess flagellated (swimming) sperm.
•Both the sporophyte and gametophyte generations are free-living.
•The gametophyte stage is greatly reduced.
•The diversity of ferns, as illustrated by a few genera of the largest order of ferns,
Filicales
•Lindsaea obtusa
•A tree fern, Cyathea, at Monteverde, Costa Rica.
•Plagiogyria, Costa Rica
•Elaphoglossum
•Asplenium septentrionale(铁角蕨）, a small fern that occurs all around the Northen
Hemisphere, growing on metal- rich soil.
•Pleopeltis polypodioides –growing as an epiphyte on a trunk in Arkansas
•Hymenophyllum（膜叶蕨） species, one of the filmy ferns. Filmy ferns occurs
as
epiphytes primarily in tropical rainforests or wet temperate regions.
•Nephrolepis cordifolia
•Nephrolepis cordifolia
•Development and structure of the two principal types of fern sporangia. (a) The
eusporangium originates from a series of superficial parent cells, or initials. Each
eusporangium develops a wall two or more layers thick (although at maturity the inner
wall layers may be crushed) and a high number of spores. (b) The leptosporangium
originates from a single initial cell, which first produces a stalk and then a capsule. Each
leptosporangium gives rise to a relatively small number of spores.
•Fern leaf (called a frond) unfolds via circinate vernation（拳卷脉序） ("fiddleheads")
from a rhizome.
•Comprising the sorus are a few to many sporangia
102
•Sectioned view of sorus with an indusium (Polystichum)（耳蕨） and without
(Polypodium)(水龙骨属）
•a. Meiosis takes place in the young sporangium in the spore mother cell (2N). The four
haploid cells resulting from meiosis divide mitotically to form first 8, 16, 32, and then
(usually) 64 spores. This marks the beginning of the haploid generation.
•b. The sporangium has special thickened cells along one side which react to changes in
humidity. The spores are dispersed by the rapid movement of the dehiscing sporangium
•c. The spores land on a suitable (moist) substrate and germinate. The threadlike
protonema has chloroplasts and continues to grow via mitotic divisions an apical cell.
Eventually, a large, heart-shaped prothallus is formed
•Eventually, a large, heart-shaped prothallus is formed (Gametophyte)
•d. The prothallus forms two kinds of sex cells in special structures. The male cells
(sperm) are formed in an antheridium.
•The female sex cell (egg) is formed in an archegonium
•Water is required to allow the motile sperm to swim to the opening of the archegonium
(drawn there by a chemical attractant)
•e. At the moment of fertilization, the nuclei of sperm and egg fuse and a diploid zygote
is formed. This begins the sporophytic generation again. The zygote divides mitotically to
form an embryo. This embryo develops tiny leaves and is at first still attached to the
notch area of the prothallus. It eventually grows much larger and looses its dependence
upon the gametophyte
•The life cycle of Polypodium, a homosporous leptosporangiate fern
103
Chapter 14 Gymnosperms
In this chapter we’ll deal with the following topics:
• Evolution of the Seed
• Living Gymnosperms
• Phylum Coniferophyta
• The Other Living Gymnosperm Phyla: Cycadophyta, Ginkgophyta, and
Gnetophyta
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What is a seed, and why was the evolution of the seed such an important
innovation for plants?
2. From which group of plants is it hypothesized that seed plants evolved?
Why?
3. How do the mechanism by which sperm reach the eggs differ in gymnosperms
and seedless vascular plants?
4. What are the distinguished features of the four phyla of living gymnosperms?
Main Characteristics of Gymnosperms
•Gymnosperms are unique because they are the only seed plants with naked ovules.
•These plants are usually woody and evergreen and can be either coniferous or
deciduous.
•Gymnosperms have a continuously growing tap root that is long lasting and provides
better anchorage in the ground than other plants.
•Another characteristic that is unique to the gymnosperms is that they are monostelic,
meaning their vascular tissue is arranged with a single stele in the center.
•A great evolutionary advantage for gymnosperms is that they are heterosporous,
meaning the sporophyte produces two kinds of spores that develop into unisexual
gametophytes.
•They do not need water for pollen dispersal, instead they rely on wind. This is
advantageous to them because it creates faster evolutionary change.
Evolution of the Seed
•Longitudinal section of an ovule, which consists of a megasporangium (nucellus)
enveloped by an integument with an opening, the micropyle, at its apical end. A single
functional megaspore is retained within the megasporangium (not shed) and will give rise
to a megagametophyte, which is retained within the megasporangium. Following
fertilization, the ovule matures into a seed, which becomes the unit of dispersal.
•Reconstruction of a fertile branch of the Late Devonian plant Elkinsia polymorpha,
showing its ovules. Each ovule was overtopped by a dichotomously branched, sterile
structure called a cupule. Note the more or less free lobes of the integument.
104
•(a) Reconstruction of a fertile branch of the Late Devonian plant Archaeosperma
arnoldii, showing four ovules. The cupules, which partly enclose the ovules, are arranged
in pairs, and each cupule contains two flask-shaped ovules about 4 millimeters long. The
apex of each integument was lobed
•(b) Diagram of the ovule, showing the position of a megaspore tetrad. The three aborted
megaspores are found at the top of the functional megaspore. The lobes of the integument
form a rudimentary micropyle. The question marks indicate the presumed position of the
nucellus.
•Seedlike structures in a number of Paleozoic plants, showing some of the potential
stages in the evolution of the integument. (a) In Genomosperma kidstonii (the Greek
word genomein means "to become," and sperma means "seed"), eight fingerlike
projections arise at the base of the megasporangium and are separated for their entire
length. (b) In Genomosperma latens the integumentary lobes are fused from the base of
the megasporangium for about a third of their length. (c) In Eurystoma angulare fusion is
almost complete, while (d) in Stamnostoma huttonense it is complete, with only the
micropyle remaining open at the top.
•A simplified summary showing the phylogenetic relationships between the major groups
of embryophytes (organisms with multicellular embryos). The embryophytes, vascular
plants, seed plants, and angiosperms are monophyletic groups, whereas the bryophytes,
pteridophytes (seedless vascular plants), progymnosperms, and gymnosperms each
contain several lineages, indicated here by a broad band, and are paraphyletic. A single
example is given of the characters that define each of the monophyletic groups.
•Phylum Coniferophyta
•The phylum with the most numerous, most widespread, and most ecologically important;
•Some 50 genera with about 550 species;
•Ovules and seeds exposed;
•Sperm nonflagellated;
•Appearance
• Branching woody plants ,needle or scale-like leaves.
Pines are conifers with a unique leaf arrangement
•Pinus resinosa View of bough of Pinus resinosa
•Most pine species retain their needles for two to four years. In bristlecone pine (Pinus
longaeva)(狐尾松）, the longest-lived tree in the White Mountains of California, the
needles are retained for up to 45 years and remain photosynthetically active the entire
time.
•The leaves of pines, like those of many other conifers, are impressively suited for
growth under conditions where water may be scare or difficult to obtain.
105
•In the stems of pines and other conifers, secondary growth begins early and leads to the
internal formation of substantial amounts of secondary xylem, or wood, which consists
primary of tracheids.The phloem consists of sieve cells, which are typical food –
conducting cells of gymnosperm.
•Microsporangiate Stages
•Cluster of Microsporangiate cones
•Whole Microsporangiate cone
•Dissected cone - view of microsporophylls
•Longitudinal section of Micsrosporangiate Cone
•Old male cones of Pinus nigra and Longitudinal view of male cone (right)
•Pollen Grains (Microgametophytes)
•Each pollen grain has two nuclei and two hollow bladders. The bladders make the pollen
grain very light and easy for the wind to blow around.
•Megasporangiate Stages
•View of Bough with Megasporangiate Cones at time of pollination
•Detail of Megasporangiate Cones at time of pollination
• View of 8-month old cone
•Whole 8-month old cone
•Dissected 8-month old cone - view of ovules
•Seed-scale Complex: detail of ovules
•Seed-scale complex: view of two sides
•Pinus.(a)Longitudinal view of young ovulate cone, showing its complex structure.
•(b) Detail of a portion of the cone. Note the megasporocyte (megaspore mother cell)
surrounded by the nucellus
•Megaspore mother cell x100. This is a first year cone. The cone axis is on the right.
An arrow indicates the megaspore mother cell in an ovule. This cell will divide by
meiosis to make four megaspores, one of which will divide by mitosis to make the
female gametophyte inside the ovule.
•
•In the female cone each scale bears two megasporangia - ovules in which a single
mother cell undergoes meiosis to produce four megaspores.
106
•One megaspore develops into the female gametophyte which contains thousands of cells
and is considerably larger than the male gametophyte.
•Male gametophyte development has to wait up to a year for the female gametophyte to
mature and produce two or three archegonia with egg cells.
•
•Second year ovule with pollen droplet x100. As the pollen droplet dries it draws
pollen into the pollen chamber of the ovule. The cone axis is on the right.
•
•Second year ovule with pollen in pollen chamber x40. In this illustration the cone
axis is on the left.
•Micropyle and pollen chamber containing pollen x100
•
•Germinating Pinus pollen grain in pollen chamber x400. Note the branched pollen
tube extending to the right. The pollen grain sits in the pollen chamber and the
micropyle is off to the left.
•Mature ovule just prior to fertilization x12. It sits on a cone scale that is attached to
the cone axis off the right side of the illustration.
•Archegonium median x40 in a mature ovule. The archegonium's neck, just above
the egg, is only two cells in length.
•Mature seed
in 3rd year cone x12. The embryo sporophyte is in the center. The
seed coat (integument) outside of the nutritive gametophyte is not shown in this
specimen.
•Longitudinal Section: view of ovule with pollen chamber and megaspore mother cell
•View of older seed scale - megagametophyte with archegonia
•View of megagametophyte with archegonia
•Embryo and Seedling Stages
•View of dissected seed showing embryo and female gametophyte
•View of dissected seed showing cotyledons
•View of longitudinal section through a seed
•View of stages of germination
•1. Cotyledons haustorial
107
•2. Cotyledons unfolding
•3. Cotyledons photosynthetic
•Because seed development takes such a long time it is often possible to find three years'
cones on pine trees
•Life cycle of a pine (Pinus; phylum Coniferophyta)
1.Most trees (sporophyte) bear female and male cones
2.Pollen cone (male) contains microsporangium, which divide by meiosis and produce
pollen grains
3.Ovulate cone (female) contains megasporangium, which are found in the ovules that are
protected by scales
4.Pollination: Pollen drawn into ovule through micropyle. Germination: forms a pollen
tube that begins its way up the nucellus
5. Megaspore mother cell undergoes meiosis and produces 4 haploid cells, one of which
survives
6. Multiple archegonia (each containing an egg) develop within the female gametophytes;
Two sperm cells develop in male gametophytes
7. Fertilization: Pollen tube grows towards female gametophyte (occurs about 1 year
after pollination)
8. Ovule develops into a pine seed, which includes:
•Embryo (new sporophyte)
•Food supply (female gametophyte tissue)
•Seed coat (derived from parent sporophyte)
•The important details of the sexual life history are shown below. The basic color code is
simple. Sporophyte cells and tissues are usually green. Sporangia are red. The
sporocytes are yellow. The spores are cyan. The gametophytes are blue. Nuclei are
magenta (when shown).
•Life cycle of a pine(Pinus; phylum Coniferophyta).
•The conifers of the yew family (Taxaceae) have seeds that are surrounded by a fleshy
cup-the aril. The arils attract birds and other animals, which eat them and thus spread the
seeds. (a) Members of the Genus Taxus, the yew-which occur around the North
Hemisphere-produce red, fleshy ovulate structure.
•The ‘big trees’ (Sequoiadendron giganteum) of California’s Sierra Nevada are the
largest of gymnosperms.The laregest specimen, the General Sherman sequoia, is more
than 80 meters high and estimated to weigh at least 2500 metric tons. The largest of
living animal, the blue whale, pales by comparison. Blue whales rarely exceed 35 meters
in length and 180 metric tons in weight.
108
•The Dawn Redwood is an ancient tree. Once thought to be extinct, it was found in
fossilized form in Japan, 1941. It was then found growing wild in China. The species is
over 50 million years old. It was introduced to the U.S. and Europe in 1948, and since has
become a favorite ornamental tree. It is one of few cone-bearing deciduous trees. It is a
member of the Redwood family (Taxodiaceae).
109
Chapter 15 Introduction to the Angiosperms
In this chapter we’ll deal with the following topics:
•
•
•
Main Characteristics of Angiosperms
The Flower
The Angiosperm Life Cycle
By the time you finish studying this chapter, you should be able to answer the
following questions:
1. What is flower, and what are its principal parts?
2. What are some of the variations that exist in flower structure?
3. By what processes do angiosperms forms microgametophytes (male
gametophytes)? How are these processes both similar to and different from
those that give rise to megagametophytes (female gametophytes)?
4. What is the structure, or composition, of the mature male gametophyte in
angiosperms? Of the mature female gametophyte?
5. What is meant by “double fertilization” in angiosperms, and what are the
products of this phenomenon?
6. What are some of conditions that promote outcrossing in angiosperms, and
under what circumstances might self-pollination be more advantageous than
outcrossing?
Main Characteristics of Angiosperms
•Flowering plants;
•Seed plants in which ovules are enclosed in a carpel and seeds are borne within fruits;
•The angiosperms are extremely diverse vegetatively but are characterized by the flower,
which is basically insect-pollinated;
•Other modes of pollination, such as wind pollination, have been derived in a number of
different lines;
•The gametophytes are much reduced, with the female gametophyte often consisting of
only seven cells at maturity;
•Double fertilization involving the two sperm of the mature microgametophyte gives rise
to the zygote (sperm and egg) and the primary endosperm nucleus(sperm and polar
nuclei);
•The former becomes the embryo and the latter becomes a special nutritive tissue called
the endosperm;
•There are about 235, 000 species.
Main Differences between Monocots and Eudicot
Characteristics
Eudicot
Monocot
1.Flower parts
In fours or fives
In threes
(usually)
(usually)
110
2.Pollen
3. Cotyledon
4. Leaf venation
5. Primary vascular
bundles in stem
6. True secondary
growth, with
vascular cambium
Triaperturae
(having three
pores or furrows)
Two
Usually netlike
In a ring
Monoaperturae
(having one pore
or furrow)
One
Usually parallel
Complex arrangement
Completely present
Rare
Monocot & Dicot Comparison
This is the tallest Flowering Plant in the world!!
•The giant eucalyptus（桉树）(Eucaluptus jacksonii),growing in the Valley of the
Giants in southwesten Australia. In size, they reach over 100 meters tall with trunks
nearly 20 meters in girth.
•The duckweeds（浮萍）(family Lemnaceae) are the smallest flowering plants.
•Dorsal
view of Lemna gibba (膨胀浮萍）in full bloom, which is about 2 to 3 mm
long.Two stamens and a short style are projecting from a lateral budding pouch at the
base of the plant. The androecium consists of two pollen-bearing stamens. The
gynoecium consists of a single pistil with a concave stigma, slender style and basal ovary
bearing a one or two ovules. The bisexual flower is enclosed within a membranous
saclike spathe within the budding pouch.
•A flowering plant of Wolffia borealis with a circular concave stigma (looking like a tiny
doughnut) and a minute anther just above it, both protruding from a central cavity. The
whole plant is less than 1 millimeter long.
•A population of Wolffia columbiana, W. borealis and W. globosa in the San Diego River
of San Diego County, California. The darker, more rounded (spherical) plants are W.
columbiana, a common South American species. The smallest plants are W. globosa,
some of which are only 0.3 to 0.5 mm in diameter, roughly the size of the world's largest
bacterium (Thiomargarita namibiensis) from the southwest coast of Africa.
•Monocots. (a) A member of the palm family, the coconut palm (Cocos nucifera),
growing in Mexico. A coconut is a drupe, not a nut
•(b) Flowers and fruits of the banana plant. The banana flower has an inferior ovary, and
the tip of of the fruit bears a large scar left by the fallen flower parts.
•( c ) Rice (Oryza sativa) is a member of the grass family.
•This species is one of the most important food crops that humans utilize, providing the
primary source of starch for a large segment of the world's population.
111
•Eudicots. (a) Saguaro cactus. (Carnegiea gigantea). The cacti, of which there are about
2000 species, are almost exclusively a New World family. The thick, fleshy stems, which
store water, contain chloroplasts and have taken over the photosynthetic function of the
leaves.
•(b) Round-lobed hepatica (Hepatica americana)(圆叶獐耳细辛）, which flowers in
deciduous woodlands in the early spring. The flowers have no petals but have six to ten
sepals and numerous spirally arranged stamens and carpels.
•(c) California poppy (Eschscholzia california)（花菱草） is the state flower of
California and is protected by law. Annual, Height : 25 - 35 cm.Easy to grow variety.
Brightly coloured flower with delicate petals. Good bedding plant which enjoys sunny
position.Sow directly in rows with 30 cm apart.Plants will flower after 45 days from
sowing.
•Parasitic and myco-heterotrophic angiosperms. These plants have little or no chlorophyll;
they obtain their food as a result of the photosynthesis of other plants.
•(a) Dwarf mistletoe (Arceuthobium campylopodum) growing on the branch of a jeffrey
pine (Pinus jeffreyi) in the Laguna Mountains of San Diego County, California. The ripe
berries are ready to explode and forcibly eject their sticky seeds.
•Dodder (Cuscuta salina)（菟丝子）, a parasite that is bright orange or yellow. A fiery
orange mass of dodder (Cuscuta californica) in the chaparral of San Diego County,
California. The host shrub, laurel sumac (Malosma laurina)（漆树） is completely
obscured by the dodder.
•Close-up view of the flowers of California dodder (Cuscuta californica) twining around
the stem of its host shrub, wild buckwheat (Eriogonum fasciculatum)（平顶绒毛蓼）.
The flowers are only 3-4 mm in length.
•Dodder (Cuscuta californica) on Sarah. This parasitic member of the Morning-Glory
Family (Convolvulaceae)（旋花科） is also known as witches' hair.
•Salt marsh dodder (Cuscuta salina var. salina) in San Diego County. Left: Host plant is
Jaumea carnosa (Asteraceae). Right: Host plant is Atriplex triangularis（摈藜）
(Chenododiceae).
•The Stinking Corpse Lily: World's Largest Flower
•The infamous “stinking corpse lily” (Rafflesia arnoldii)（大花草）, the world's largest
flower. This remarkable Malaysian/Indonesian endoparasite lives completely within its
host vine, and occasionally breaks through the bark as a huge bud that expands into an
enormous blossom 3 feet (0.9 m) across
•Pilostyles thurberi, a minute parasitic wildflower native to the Colorado Desert of the
southwestern United States. Like its monstrous Asian counterpart, Rafflesia arnoldii, it
lives completely within the stem of its host shrub. The head of a pine shows the small
size of the blossoms.
112
•Indian pipe (Monotropa uniflora)（水晶兰）, a myco-heterotroph that obtains its food
from the roots of other plants via the fungal hyphae associated with its roots. There are
more than 3000 species of parasitic angiosperms, representing 17 families.
•Bisexual flower showing all 4 characteristic parts which are technically modified leaves:
Sepal, petal, stamen & pistil. This flower is referred to as complete (with all 4 parts) and
perfect (with "male" stamens and "female" pistil). The ovary ripens into a fruit and the
ovules inside develop into seeds. Most flowers contain several to many ovules.
Incomplete flowers are lacking one or more of the 4 main parts.
The Remarkable Bisexual Milkweed Blossom
The Remarkable Bisexual Orchid Blossom
•Detailed view of the blossom of a spider orchid (Brassia hybrid) showing the major
perianth segments and central column.
Inflorescence
•An inflorescence may be defined as a cluster of flowers, all flowers arising from the
main stem axis or peduncle
Inflorescence Definitions
•Inflorescences with youngest flower at the end of the main axis (rachis) are called
"indeterminate" (i.e. terminal bud continues to produce new flowers).
• Inflorescences with oldest flower at the end of the main axis are called "determinate"
(i.e. terminal bud stops growing and lateral flowers are produced from axillary buds.)
Inflorescence Types
Cyme（聚伞花序）
•紫草科和田基麻科
•Two species of Family Boraginaceae
•Cyme（聚伞花序）- an inflorescence in which each flower, in turn, is formed at the tip
of a growing axis and further flowers are formed on branches arising below it. Note that
in this inflorescence of bouncing bet (Saponaria officinalis)（肥皂草） the largest and
oldest flower (the one in longitudinal section) is in the center, with younger flowers on
either side and below.
•Another example of a cyme. This is of burning bush (Euonymus alata, 卫矛 ).
Inflorescences that are basically cymes are very common in plants, yet most cymes are
modified in some way. Usually, flowers on one side of a branch are suppressed.
•Umbel（伞形花序）
•The Umbel of Cicuta maculata (斑点毒芹）
113
•Umbel inflorescence in which all the individual flower stalks arise in a cluster at the top
of the peduncle and are of about equal length. This example is blood-flower (Asclepias
currassavica)（马利筋）.
•Compound umbel-instead of individual flowers radiating out from a single point, there
are inflorescence branches. At the ends of each branch are secondary umbels. This
example is wild carrot (Daucus carota)（胡萝卜）.
•Corymb（伞房花序）- a racemose inflorescence in which the pedicels of the lower
flowers are longer than those of the flowers above, bringing all flowers to about the same
level. This example is Viburnum lantana（绵毛荚迷）.
Capitulum（头状花序）: Inflorescence Of The Sunflower Family
•A capitulum or head, the characteristic inflorescence of the sunflower family
(Asteraceae)（菊科）. Depending on the tribe, the inflorescence may consist of ray
flowers, disk flowers, or both ray and disk flowers. The ovary of each flower is situated
below the attachment of the corolla and stamens, a condition referred to as epigynous or
inferior. This is the largest family of flowering plants with approximately 24,000 species.
•Close-up view of a portion of the large flowering head of a sunflower (Helianthus
annuus) showing an outer ring of large, strap-shaped (petal-like) ray flowers surrounding
a dense mass of small, tubular disk flowers. The ovaries of the disk flowers ripen into the
achenes sold in markets as sunflower seeds. The entire head is subtended by green,
overlapping bracts called phyllaries.
•Head or Capitulum- an inflorescence with sessile flowers aggregated into a dense
cluster like the head of a pin. Characteristic of the aster（紫菀） or sunflower family
(Asteraceae). In the photos on the left are several heads of Short's aster (Aster shortii),
while on the right is a longitudinal section of a single head. In this particular kind of head,
there are two types of flowers-ray and disc.
•Spike（穗状花序）- an unbranched, indeterminate inflorescence in which the flowers
are without pedicels, that is the flowers are sessile.
•Both of these spikes are from prairie plants. On the left is Culver‘s root (Veronicastrum
virginicum)（弗吉尼亚草本威灵仙） and on the right is scented ladies’ tresses orchid
(Spiranthes magnicamporum，绶草). Note the bracts at the base of each flower.
•Raceme（总状花序）- an indeterminate inflorescence in which a main axis produces a
series of flowers on lateral stalks, the oldest at the base and the youngest at the top. The
example on the left is black cherry (Prunus serotina)（野黑樱） and the one on the right
is field-cress (Lepidium campestre)（田野独行菜）.
114
•Panicle（圆锥花序）- a compound raceme; an indeterminate inflorescence in which
the flowers are borne on branches of the main axis or on further branches of these. The
example on the left is meadow-sweet (Spiraea latifolia)（宽叶绣线菊）, the one in the
middle is Meyer lilac (Syringa meyeri，蓝丁香), and on the right is Yucca gloriosa L
（风尾丝兰）.
•
•Syconium: Inflorescence Of The Figs (Ficus)
•Syconium（隐头花序）: A hollow, spherical or flask-shaped inflorescence lined on the
inside with numerous minute, apetalous, unisexual flowers. Male flowers consist of one
to five stamens, while female flowers consist of a single pistil (gynoecium) with a long or
short style. The flowers are pollinated by minute symbiotic female wasps that enter the
syconium through a pore (ostiole).
•The syconium is a complex inflorescence (flower cluster) consisting of a hollow, fleshy
structure (peduncular tissue) lined on the inside with numerous tiny unisexual flowers.
The ripe syconium is not a true fruit in the strict botanical sense. It is actually a fleshy,
flask-shaped, modified stem lined on the inside with many tiny one-seeded fruits. The
mature fig syconium is also called a multiple fruit because it is composed of numerous
ripened, seed-bearing ovaries derived from numerous female (pistillate) flowers.
•Female catkin（柔夷花絮） from a variety of black mulberry (Morus nigra)（黑桑）.
Mulberry flowers are produced in a catkin, with male and female catkins on different
trees. Male flowers have four stamens while female flowers consist of single pistil tightly
enveloped by four inconspicuous sepals. Each carpel or pistil (also referred as a
gynoecium) consists of a forked stigma, a short style and a spherical ovary. Each ovary
(carpel) becomes a drupelet and the ripened cluster of drupelets (syncarp) is called a
multiple fruit. In the aggregate fruit of a blackberry, all the drupelets of the cluster
(syncarp) come from a single flower. Seedless fruits may be produced without pollination
by male trees.
•Catkin: Inflorescence With Unisexual Flowers
•Left: Male (staminate) catkin from the white mulberry (Morus alba), a fruitless variety
commonly planted as a shade tree in southern California. Right: An individual male
flower containing four stamens, each with an anther and a filament. At the base of each
filament is a fleshy green sepal. Male trees are known as "fruitless mulberry" because
they do not produce messy fruits that stain clothing and walkways.
•The Ovules are Attached to the Ovary Wall at the Placenta
•Cross section of the ripened ovary (fruit ) of a bell pepper (Capsicum annuum) showing
three locules (chambers) and axile placentation. The central region where the seeds are
attached is the placenta. In hot chile peppers, the placental region contains up to 89
percent of the alkaloid capsaicin. This alkaloid causes a burning sensation when it comes
in contact with the sense receptors in your tongue.
115
•Color variation in bell peppers (Capsicum annuum). In some cultivars the green peppers
ripen to a deep red. In other varieties, green peppers ripen to a golden yellow or bright
orange.
•In parietal placentation, there is one locule and as many placenta attached to the ovary
wall as there are carpels. In this example, note the numerous ovules attached to each
placenta; the plant is Euclid bartonioides.
•Basal placentation: one or more ovules are attached to the bottom of the ovary. This
situation is found for example in some Portulacaceae （马齿苋科） like Portulaca（马
齿苋） (photo on the left; the yellow arrow is pointing to the ovules) or in Talinum（土
人参属） (close up on the right; the black arrow is pointing to the placenta). The ovary is
unilocular.
•Free-central — a placentation type in which the ovules are borne on a free-standing
central placenta within the ovary. This example is primrose (Primula cultivar)（报春
花）.
There are many variations in flower structure
Ovary Position
•Types of flowers in common families of eudicots, showing differences in the position of
the ovary.(a) In Ranunculaceae, the buttercup family, are said to be hypogynous. In
contrast, , many Rosaceae, such as cherries are said to be perigynous.
•The flowers of other plants, for example Apiaceae, the parsley family（欧芹科）, are
said to be epigynous
•An ovary is said superior when it is situated above the point of attachment (=insertion)
of the perianth and androecium and free from them, as in this longitudinal section of a
flower of mustard (Brassica species).
•This photo of Solomon’s seal (Polygonatum commutatum)（大黄精） shows another
example of a superior ovary and hypogynous insertion. Note here that the perianth
consists of tepals (since you cannot distinguish between sepals and petals), to which the
stamens are adnate.
•In the genus Rosa, flowers have a deep hypanthium, with many carpels, free (not fused
with the hypanthium) and distinct (apocarpous gynoecium). Each of these carpels has a
superior ovary, enclosed in the hypanthium. Here again, the insertion is perigynous. The
styles protrude through the opening in the top of the hypanthium.
116
•An ovary is said to be inferior when it is situated below the apparent point of attachment
of the outer floral parts, as on this close up of a longitudinal section of apple, Malus.
•The perianth and androecium are ADNATE to the gynoecium. Relative to the ovary the
insertion of the perianth and androecium is epigynous.
•Epigynous — of floral parts (especially petals and stamens), attached above the level of
insertion of the ovary and arising from tissue that is fused to the ovary wall.
•This longitudinal section of a flower of Fuschia sp.（倒挂金钟） shows another
example of inferior ovary and epigynous insertion.
•Perigynous（子房上位周位花） — of perianth segments and stamens, arising from a
hypanthium that is free from the ovary but extending above its base.
•When the perianth and the stamens arise from a hypanthium that is NOT adnate to a
superior ovary, the insertion is said to be perigynous, as in this longitudinal section of a
flower of black cherry Prunus serotina（野黑樱）.
Flower Symmetry
•A dissected flower of Erythrina cristagalli （海红豆）showing all the major perianth
segments removed from their attachment inside the calyx. The five petals consist of one
large, oval banner or standard, two elongate keel petals that are fused together enclosing
the stamens, and two reduced wings. Nine stamen filaments are united into a sheath that
surrounds the pistil. One stamen filament is separate from the fused nine, a condition
referred to as diadelphous stamen(二体雄蕊）
•Actinomorphic (Regular): Flower with radial symmetry because the perianth segments
(petals and sepals) are similar in size and shape. This type of flower is divisible into equal
halves along more than one plane. Here is an example of actinomorphic flower. In this
case the floral parts are numerous. This example is a water lily (Nymphaea cultivar).
•A zygomorphic (irregular) flower has a bilateral symmetry — it can be divided in two
equal halves by only one plane, as shown by the red line passing through this flower of
Viola tricolor（三色堇）.
•Microsporogenesis and Microgametogenesis Culminate in the Formation of Sperm
•Two distinct processes-microsporogenesis and microgametogenesis-lead to the
formation of the microgametophyte.
•Microsporogenesis is the formation of microspores (single-celled pollen grains) within
the microsporangia, or pollen sacs, of the anther.
•Microgametogenesis is the development of the microgametophyte within the pollen
grain up to the three-celled stage of development.
•a young flower bud of Lilium cut in cross section
117
•Note the single compound pistil in the centre of the section. The pistil is composed of
three fused carpels. Two dense staining ovule primordia are evident in each of the three
locule. Outside the pistil are six bilobed anthers, three petals and three sepals.
•Two transverse sections of Lily (Lilium) anthers. (a)Immature anther, showing the four
pollen sacs containing microsporocytes surrounded by the nutritive tapetum
•(b) Mature anther containing pollen grains. The partitions between adjacent pollen sacs
break down during dehiscence, as shown here.
•Microspore tetrad.
•As anther development proceeds, the microsporocytes divide by meiosis to produce a
spherical tetrad of four microspores
•Mature pollen grain of Lilium, containing a two-celled male gametophyte. The spindleshaped generative cell will divide mitotically after the germination of the pollen grain.
The large tube cell, which contains the generative cell, will form the pollen tube.
•Pollen – Dandelion(蒲公英） SEM
•When the pollen grain lands on the stigma , the generative nucleus divides to form two
sperm nuclei
Megasporogenesis and Megagametogenesis Culminate in Formation of an Egg and
Polar Nuclei
•Two distinct process-megasporogenesis and megagametogenesis-lead to the formation
of the megagametophyte.
•Megasporogenesis is the process of megaspore formation within the nucellus
(megasporangium), which takes place inside the ovule.
•Megagametogenesis is the development of the megaspore into the megagametophyte
(female gametophyte, or embryo sac).
•Lilium. Some stages in development of an ovule and embryo sac. (a-1) Two young
ovules, each with a single, large megasporocyte surrounded by the nucellus. Integuments
have not begun to develop.
•(a-2) Close- up of one of the young ovules
•(b) Ovule has now developed integuments with a micropyle. The megasporocyte is in
the first prophase of meiosis.
•(c) Ovule with eight nucleate embryo sac (only six of the nuclei can be seen here, four at
the micropylar end and two at the opposite, chalazal end). The polar nuclei have not yet
migrated to the center of the sac. The funiculus is the stalk of the ovule.
Pollination and Double Fertilization in Angiosperms are Unique
•With dehiscence of the anther-that is , shedding of its contents-the pollen grains are
transferred to the stigmas in a variety of ways;
•The process whereby this transfer occurs is called pollination.
118
•Pollination mechanisms
•In order for a flower to be pollinated, pollen must be moved from the anthers to the
stigma of the same or different flowers. The pollen can be moved in different ways.
•wind
water
insects
mammals
birds
Characteristic features of wind pollinated flowering plants include:
•They produce huge amounts of non sticky pollen
•They often lack a large and showy calyx or corolla
•They have many flowers packed into a inflorescence
•They have large stigmas
•They have large, well exposed anthers
Identification Of Major Fruit Types
•I. Simple Fruits: A fruit derived from one carpel or several united carpels.
•A. Fleshy Fruits: All of, or most of the ovary wall (pericarp) is soft or fleshy at maturity.
•B. Dry Fruits: Pericarp dry at maturity.
•1. Dehiscent Dry Fruits: Pericarp splits open along definite seams.
•2. Indehiscent Dry Fruits: Pericarp does not split open. These fruits usually contain only
one seed.
•II. Aggregate Fruits:
•A fruit developing from the several separate carpels of a single flower.
•In blackberries, strawberries and raspberries (Rubus)(悬钩子）, the individual fruits are
tiny, one-seeded drupes or drupelets.
•The individual parts of aggregate fruits are known as fruitlets.
•Aggregate Fruit: Many ovaries derived from a single flower.
•Aggregate fruit of a hybrid strawberry (Fragaria xananassa) showing the individual
yellowish-brown, one-seeded achenes embedded in the red, fleshy receptacle. Although
the one-seeded achenes represent separate ripened ovaries, each strawberry is produced
from a single white flower bearing many stamens.
•Aggregate fruit of a hybrid strawberry (Fragaria
xananassa) showing the individual
yellowish-brown, one-seeded achenes embedded in the red, fleshy receptacle. Although
119
the one-seeded achenes represent separate ripened ovaries, each strawberry is produced
from a single white flower.
•Flower and aggregate fruit of thimbleberry (Rubus parviflorus)(糙莓）, a native shrub
in the mountains of the western United States. Although the tiny, one-seeded drupelets
represent separate ripened ovaries, each aggregate cluster of fleshy drupelets developed
from a single white flower.
•Aggregate fruits of a blackberry (Rubus ursinus) in coastal northern California showing
the individual drupelets, each with a separate style. Although the one-seeded drupelets
represent separate ripened ovaries, each aggregate cluster of drupelets develops from a
single white flower.
•Aggregate fruits of the raspberry（悬钩子）, a commercially-grown hybrid of (Rubus
idaeus). Although the one-seeded drupelets represent separate ripened ovaries, each
aggregate cluster of drupelets develops from a single white flower. Note the individual
hair-like styles that arise from each of the numerous drupelets. The most obvious
difference between these fruits and blackberries is their red color.
•
•III. Multiple Fruits:
•A cluster of many ripened ovaries (fruits) produced by the coalescence of many flowers
crowded together in the same inflorescence, typically surrounding a fleshy stem axis. E.g.
mulberry, pineapple.
•In the mulberry (Morus), the individual fruits are tiny drupes called drupelets.
•In the pineapple (Ananas), the individual fruits are berries imbedded in a fleshy, edible
stem, each berry subtended by a jagged-edged bract where the original flower was
attached.
•Black mulberry (Morus nigra), a dioecious tree native to western Asia. The bumpy
surface of the fruit is due to many tightly-packed, seed-bearing ovaries (drupelets), each
with separate styles that appear like black hairs. It is technically a multiple fruit (called a
syncarp) composed of a cluster of drupelets superficially resembling a blackberry;
•Three examples of multiple fruits: A. Jackfruit (Artocarpus heterophyllus)（木菠萝）;
B. Pineapple (Ananas comosus); and C. Breadfruit (Artocarpus altilis). All three fruits
are refered to as "multiple fruits" because they are derived from the coalescence of
ovaries from many individual flowers plus a fleshy stem axis.
•I. Simple Fruits-A. Fleshy Fruits:
•1. Berry: All or most of pericarp fleshy
•Although it is called a "vegetable," the tomato (Lycopersicon esculentum) is technically
a botanical fruit referred to as a berry. Most of the interior tissue of a true berry is soft
and fleshy.
120
•Two popular varieties of seedless grapes in California: 'Thompson Seedless' (left) and
delicious 'Red Flame' (right). Grapes are considered a true berry because the entire
pericarp (fruit wall) is fleshy.
•Grape vineyard in the Napa Valley wine country of California
•Pomegranate: An Unusual Berry
•Pomegranate (Punica granatum), showing persistent calyx at the top of fruit. The calyx
is cut away on right fruit to show the numerous stamens. The fruit is technically a
leathery-skinned berry containing many seeds, each surrounded by a juicy, fleshy aril.
The pomegranate tree is native to Africa and the Near East.
•The persimmon fruit is a true berry because the pericarp is fleshy all the way through,
without a endocarp layer as in drupes.
•Farmer Howell Sonoda standing behind his new crop of air-dried 'Hatchiya' persimmons
(Diospyros kaki). The sweet dried fruit is delicious and tastes like candy.
•The Avocado（鳄梨）
•The fruit is a berry, consisting of a single large seed, surrounded by a buttery pulp. Fruit
contain 3 to 30% oil (Florida varieties range from 3 to 15% oil). The skin is variable in
thickness and texture. Fruit color at maturity is green, black, purple or reddish, depending
on variety. Fruit shape ranges from spherical to pyriform, and the fruit weigh from a few
ounces to 5 lbs (2.3 kg). The fruit does not generally ripen until it falls or is picked from
the tree.
2. Pepo：瓠果 Berry with a hard, thick rind; typical fruit of the gourd family
(Cucurbitaceae). E.g. watermelon, cucumber, squash, and pumpkin.
The watermelon is a good example of a pepo, a berry with a hard, thick rind. This is a
triploid, seedless "yellow watermelon" (Citrullus lanatus var. lanatus). Although it is sold
as "seedless," there are some seeds in the fleshy interior.
•The World's Largest Fruit
•In October 2002, a pumpkin was reported with an astonishing weight of 1337 pounds.
•A field of pumpkins and Mr. Wolffia celebrating Halloween.
•Pumpkin harvest at Bates Nut Farm in Valley Center, California
•3. Hesperidium: （柑果）Berry with a leathery rind and parchment-like partitions
between sections; typical fruit of the citrus family (Rutaceae). E.g. orange, lemon,
grapefruit, and kumquat.
•The lemon (Citrus lemon) is a hesperidium, a berry with a leathery rind. The exocarp
(peel) contains volatile oil glands (essential oils) in pits. The fleshy interior (endocarp) is
composed of separate sections (carpels) filled with fluid-filled sacs (vesicles) that are
actually specialized hair cells.
•Close-up view of the peel (exocarp) of a lemon (Citrus lemon) showing numerous pits
containing volatile oil glands. Essential oils (terpenes and phenolic compounds) in the
pits are responsible for the aroma given off when the peels are bruised. The fragrant
121
perfume called bergamot comes from the fruit rinds of Citrus bergamia (C. aurantium ssp.
bergamia).
•Magnified longitudinal view of the endocarp of an orange (Citrus sinensis) showing
several sections (carpels) filled with numerous fluid-filled "juice sacs." The two lower
sections each contain a seed which is surrounded by the fleshy sacs. The sacs (vesicles)
are actually swollen (plump), specialized hairs.
•4. Drupe: Fleshy fruit with hard inner layer (endocarp or stone) surrounding the seed.
E.g. peach, plum, nectarine, apricot, olive, mango and almond.
•A 'California' peach (Prunus persica), a freestone peach grown in California's fertile
Central Valley. The fruit is called a drupe because it is composed of three distinct layers:
An outer skin or exocarp, a fleshy middle layer or mesocarp, and a hard, woody layer
(endocarp) surrounding the seed. The lower pit (removed from another peach) has been
sectioned to show the thick, woody layer or endocarp surrounding a single seed.
•The mango (Mangifera indica) is a drupe with an outer leathery skin (exocarp), a fleshy
mesocarp and a hard, stony endocarp (pit) surrounding the large seed.
•5. Pome: Accessory fruit with thick hypanthium.
•Ovary or core surrounded by edible, fleshy receptacle tissue (hypanthium or fleshy floral
tube) that is really not part of the pericarp. The actual ovary or core is usually not eaten,
at least by most humans. This is typical fruit of certain members of the rose family
(Rosaceae), including apple, pear and loquat.
I. Simple Fruits-B. Dry Fruits-1. Dehiscent Dry Fruits: Pericarp splits open along
definite seams.
•1. Legume or Pod: Composed of one carpel.
Note: Some legumes are indehiscent and do not split open.
•A legume (such as a bean pod) is composed of one folded carpel. It splits lengthwise
along two seams into two sections, each of which represents half of a carpel. Some
legume pods, such as carob and peanut, are indehiscent and do not split open.
•The peanut (Arachis hypogea) is a dehiscent legume that is harvested from below the
soil. The legume was originally formed above ground following pollination. After
fertilization, the flower stalk of the peanut curves downward, and the developing pod is
forced into the ground by the proliferation and elongation of cells under the ovary. The
pod typically contains two seeds, each with a papery seed coat.
•2. Capsule: （蒴果） Composed of several fused carpels
•The separate carpels of a true capsule were originally fused together to form the pistil or
gynoecium. They separate along the septa or along the locules between septa.
•Four methods of dehiscence in capsules: The carpels may separate along the septa or
along the locules between the septa. Some capsules dehisce by a lid that falls off
exposing the seeds. Poppies of the genus Papaver, including the opium poppy (P.
122
somniferum), dehisce by small apical pores near the top of the capsule. As the capsule
moves back and forth in the wind, the seeds are released like a pepper shaker.
•Mature seed pod of the opium poppy (Papaver somniferum) with milky latex sap
dripping from a recent cut. The latex sap contains a mixture of naturally-occurring
narcotic alkaloids including morphine and codeine. Morphine is acetylated to produce
diacetylmorphine, better known as heroin.
•3. Follicle: （骨突果） One carpel that splits along one seam.
•The single carpel of a follicle splits open along one seam. When completely opened, the
carpel resembles a thick, dried leaf. It is easy to see that the single carpel of a follicle is a
modified, seed-bearing leaf (megasporophyll).
•Large blossom of the southern magnolia (Magnolia grandiflora), a beautiful shade tree
native to the southeastern United States. The numerous sepals and petals are called tepals
because they are similar in size and shape. The conelike receptacle in the center is
composed of numerous spirally arranged carpels above numerous spirally arranged
stamens.
•Conelike receptacle bearing numerous follicles. Each follicle has split open and the seed
has fallen out. Conelike fossils similar to magnolia receptacles have been discovered in
ancient sedimentary strata, indicating that this is a very primitive plant family.
•Conelike receptacle of Magnolia grandiflora bearing numerous follicles. At maturity
(December in southern California), each follicle bears a bright red seed. The seeds often
hang out of the individual follicles by their long, threadlike stalks (funiculi).
•4. Silique: Two carpels separated by a seed-bearing septum.
•The silique is an elongate fruit composed of two carpels separated by a seed-bearing
partition. The silicle is very similar except it is much shorter (less than twice as long as
broad). Siliques and silicles have parietal placentation. They are the characteristic fruits
of the mustard family (Brassicaceae)
•The overlapping seeds of bitter cress (Cardamine)碎米荠 are connected to alternate
edges of the septum within each locule. The minute seeds are attached to both margins of
the central septum.
•The seeds of water cress (Rorippa nasturtium-aquaticum) are connected along both
margins of the septum within each locule.
•Inflorescence (raceme) of shepherd's-purse (Capsella bursa-pastoris), a common
European annual that is naturalized in southern California. The silicles are inverted heartshaped (obcordate). The membranous partitions remain on the pedicels long after the
valves of the silicles have fallen away.
123
•Moonwort (Lunaria annua), a European annual or biennial naturalized in California. The
fruits of this species are called silicles because they are broad compared with the elongate
and slender siliques. Generally silicles are only twice as long as broad (or less). The
septum of each silicle remains attached to the dried flower stalk, long after the valves and
seeds have fallen away.
2. Indehiscent Dry Fruits: Pericarp does not split open. These fruits usually contain
only one seed.
•The achene is the typical fruit of the sunflower family (Asteraceae). It is a small, oneseeded fruit containing a single seed. The seed is attached by a funiculus, but the seed
coat is free from the inner wall of the pericarp.
•Achenes of the sunflower (Helianthus annuus). One achene has been sectioned to
reveal the single seed inside. The seed is essentially free within the pericarp wall, except
where it is attached at the placenta. Sunflower seeds of this variety with striped pericarps
is used primarily for food. Seeds from achenes with solid black pericarps are used for
sunflower oil.
•Inflorescence and mature, seed-bearing head of the Eurasian dandelion (Taraxacum
officinale). The slightest gust of wind catches the elaborate crown of plumose hairs,
raising and propelling each seed-bearing achene into the air like a parachute. This
successful weed thrives in a wide range of climates and has become naturalized
throughout North America.
•One-seeded achenes of buckwheat (Fagopyrum esculentum, 荞麦), an important crop
plant native to central Asia. The three-sided achenes resemble miniature nuts from the
beech tree.
•2. Anthocarp: Small, one-seeded fruit enclosed by a fused perianth or receptacle.
•Two anthocarps of the desert sand verbena (Abronia villosa var. villosa). Each
seed-bearing ovary (achene) is tightly encased within the persistent winged calyx.
3. Grain (Caryopsis): One-seeded fruit; pericarp fused with seed coat.
Rice (Oryza sativa). A. Grain-bearing spikelet showing a pair of slender basal bracts
(glumes) and the stalk (pedicel). The inflorescence is composed of numerous spikelets,
each bearing a rice grain. B. An empty spikelet with the lemma and palea slightly
separated from each other. These two leathery bracts enclosed the grain or caryopsis. C.
A grain (caryopsis) removed from spikelet (B).
•Longitudinal section of a rice grain showing the embryo (germ), pericarp (bran ) and
endosperm. In polished white rice, the nutritious germ and outer bran layers are removed.
The seed coat is completely fused with the pericarp and is not visible in this image as a
distinct layer.
124
4. Samara: One-seeded, winged achene.
•The samara is a peculiar one-seeded fruit similar to an achene except the pericarp wall
extends into a thin, papery wing. The above image shows two strikingly different samaras,
one from the tree of heaven (Ailanthus altissima， 臭椿) and the other from big-leaf
maple (Acer macrophyllum).
•Evergreen or ash (Fraxinus uhdei，岑树), a beautiful ash tree native to Mexico and
commonly planted in southern California. During the summer months it produces masses
of slender, winged, one-seeded fruits (called samaras) that fly through the air like a
squadron of miniature helicopters.
5. Nut: One-seeded fruit with hard pericarp.
•The one-seeded nut of an acorn sits in a cup-shaped involucre composed of numerous
overlapping scales. These acorns are from the cork oak (Quercus suber), the bark of
which is the source of natural cork.
•The true nuts of the chestnut (Castanea dentata) are produced in a spiny, cup-shaped
involucre.
•The American filbert (Corylus americana) of the eastern United States produces a oneseeded nut enclosed in an involucre of leafy bracts. In the closely-related species of the
Pacific northwestern United States (C. cornuta), the nut is produced in an elongate,
tubular involucre.
•6. Schizocarp: （分裂果） Seed-bearing carpels split apart, but remain indehiscent.
•The schizocarps of sweet fennel (Foeniculum vulgare) are produced in clusters called
umbellets, This is typical of plants in the carrot family (Apiaceae). Each schizocarp splits
apart into two indehiscent, seed-bearing mericarps, each attached to a stalk called a
carpophore.
•Schizocarps of fennel (Foeniculum vulgare), each splitting apart into two indehiscent,
one-seeded carpels called mericarps. This valuable herb has edible, licorice-flavored leaf
stalks and seeds. Ground or whole fennel seeds are used in stuffings, sausages, breads,
cookies, cakes, candies and liqueurs.
•7. Utricle: （胞果）Small, bladderlike, thin-walled indehiscent fruit.
•Utricles of the duckweed family (Lemnaceae). The utricle is a small, bladderlike, thinwalled fruit. It is often compared with a one-seeded achene, except the utricle has a
pericarp that is loose and fragile.
125
126
127