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Plants - General
it contains the “Big Baobab Pub” built inside it
the plant and animal kingdoms are the best known
of all the kingdoms of life on earth
!tallest life form:
coastal redwood = 385’ tall[117M]
taller trees have been reported but not verified:
they show a much more complex level of organization
-a Douglas fir exceeding 400’
!both are comprised of many cells (there are NO unicellular
plants OR animals)
-a Australian mountain ash at 436’
!in most plants and animals the cells have specialized into
various tissues and the tissues into organs for greater
efficiency
!plants are some of oldest organisms on earth:
eg. sacred fig (Ficus religiosa) 2293 yrs old
plants are very diverse in size, shape and complexity
eg. Sequoias are 2000-3000 years old; oldest known is
3,200 years
today, range in size from microscopic pondweeds to
giant sequoias:
eg. oldest bristlecone pine was 4844 years old when
felled in 1964
!one of world’s most massive organism:
“general Sherman’ (giant sequoia in California)
272’ tall [81-5M]
eg. a baobab tree has been carbon dated to 6000
yrs old (doesn’t produce growth rings)
eg. new record holder is a Norway Spruce discovered in
Sweden that had a relatively young trunk; but its
roots were dated to 9,550 years - it apparently
began growing as soon as land appeared after
the last ice age
79’ girth (>25’ dia)
volume: 52508 ft3 (148 trillion m3 )
weight: 2,100,000 kg (~2000 tons)
(>10x’s heaver than blue whale=180,000kg
(~200 tons))
many plants grow in clonal colonies and
while individuals of the clone have
relatively short lifespans some clones
appear to be much older (but no hard
evidence yet):
estimated to contain over 600,000 board feet of
timber; enough to build 120 average size homes
also, Baobab Tree in South Africa is 72 ft tall
but 155’ in circumference
Plants: Introduction; Ziser Lecture Notes, 2010.8
eg. some creosote bush colonies may live up to
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Plants: Introduction; Ziser Lecture Notes, 2010.8
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Major Characteristics of Plants
11,700 yrs
eg. Eucalyptus (Eucalyptus recurva) groves may live
13,000 yrs
Members of the Plant Kingdom (Metaphyta) share the
following characteristics:
eg. Kings lomatia (Lomatia tasmanica) an Australian
tree that produces colonies is claimed to be
43,600 years old
1. All plants are multicellular
eg. quaking aspen ( Pando sp.). one grove may
contain 47,000 trees, cover 43 ha and weighs
6,500 tons (6,000,000 kg)
typical plant cells:
are eukaryotic
eg. some Aspen clones may be as old as 80,000 yrs
surrounded by cell wall
eg. large underwater meadows of Posidonia oceanica,
a seagrass in the Mediterranean may be up to
100,000 years old
many have chloroplasts for photosynthesis
2. plants are nonmotile
!subjects plants to dictates of nature
! primary influence on most of a plants characteristic
adaptations
!must be able to withstand fluctuations in
light, temperature, water availability, space &
nutrients
3. most plants are autotrophs (photosynthesis)
while diverse in form, almost all plants are similar
in function:
use the sun’s energy to make organic food from
simple inorganic nutrients; nitrogen,
phosphorus, CO2, etc.
Plants: Introduction; Ziser Lecture Notes, 2010.8
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Plants: Introduction; Ziser Lecture Notes, 2010.8
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photosynthesis to make food
but some store oils instead or in addition to starch
CO2 + H2 O + sunlight ! sugars + O2
a few are parasitic or saprophytic and some of
these cannot do photosynthesis and must “eat”
organic food
eg. a few plants are parasitic on other plants or on fungi
and do not do photosynthesis; they get all their
nutrition from their host
cellulose is found in the cell walls of all plants
cellulose comprises ~70% of land biomass
! saprobe, no photosynthesis
b. lignin is also one of the 4 most common natural
polymer
! pollinated by tiny flies that gain access via mud
cracks in dry season
ligning is found in cell walls of some plants and in the
wood of perennial plants as well as in many
seeds
a few plants, while autotrophs, are carnivorous
! they eat insects and other animals
comprises ~25% of land biomass
they usually grow in nitrogen poor soil
very difficult to degrade, mainly only by certain
species of fungi
! use nitrogen in proteins of animals they catch
presence of lignin helps to make cellulose difficult to
digest or extract for commercial uses
4. plants use aerobic respiration to extract energy
from that food
c. plants also produce a variety of chemicals such as
alkaloids, tannins, volatile oils, resins that are used
for defense, communication, coordination of plant
activities, waste disposal
sugars + O2 ! CO2 + H2 O + energy
can’t do anaerobic respiration like bacteria
! have to have O2
7. most plants have true tissues and true organs
5. most plants store excess foods as starch
tissues = groups of specialized cells performing common
function
(a complex carbohydrate)
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Plants: Introduction; Ziser Lecture Notes, 2010.8
all plants begin with primary growth
organs = groups of tissues working together to perform a
common function
herbaceous plants have only primary growth
Animals are the only other kingdom with true tissues and
true organs
annuals: live 1 year only
eg. beans, grasses, many wildflowers
8. Plants have simple responses to environmental
stimuli
biennials: require two growing seasons to
complete their life cycle
a. plants are nonmotile but do show some
simple movements:
eg carrots, cabbage, beets, etc
b. secondary growth (woody)
!sunflowers and others turn leaves or flowers to
track sun during day
wood and bark replace the softer
herbaceous tissues of the stem and
main roots
!sensitive plants close their leaves when touched
!vines and tendrils wrap around supports
perennials (=plants that grow for more than 2
years) produce secondary growth in the
stem and roots
!insectivorous plants close leaves to trap insects
! sleep movements
b. many plants also can make slower, more
permanent, changes in orientations
=tropisms
eg. all trees & shrubs
sometimes just the roots are perennial
!above ground parts dies back each winter
eg. phototrophism (light)
some plants may be annual in one climate
and perennial in another climate
eg. geotropism (gravity)
10.Many plants show a distinctive alternation of
generations between sexual and asexual
stages
eg. thigmotropism (touch)
9. plants have two different kinds of growth
related to the length of their life cycle:
plants (& some algae, fungi, and animals) have a life
cycle which consists of two completely different
forms
a. primary growth (herbaceous)
Plants: Introduction; Ziser Lecture Notes, 2010.8
a. cellulose & lignin are the primary chemicals used by
plants for support and protection.
cellulose is the most abundant natural polymer in the
world
eg. one species of orchid is known to be the only
“underground” plant
Plants: Introduction; Ziser Lecture Notes, 2010.8
6. plants produce several distinctive or unusual
chemicals:
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Most Fundamental Values of Plants:
both forms reproduce, 1 sexually and
the other asexually
human live is tightly interwoven, directly & indirectly,
into the activities of plants:
the stage that reproduces asexually is called
the sporophyte
1. all land based animal life is dependent on
plants as beginning of food chains (primary
producers)
!it produces asexual spores
the stage that reproduces sexually is called
the gametophyte
2. plants also produce & maintain about 30% of
all oxygen (O2) in our atmosphere.
(gametes are the sex cells; egg & sperm)
the other 70% is produced by marine algae and
photosynthetic bacteria
In some plant groups they exist as completely separate
entities
3. plants play a vital role in the carbon cycle
gametophyte
male
eg. 1 acre of corn (.4ha) ~10,000 plants
! accumulates >5000 lbs of Carbon from CO2 during
the growing season
female
[Haploid]
egg
asexual
spores …………………………………
[Diploid]
sperm
! equiv to >11 tons of Carbon Dioxide
fertilization
absorption by plants is balanced by production of CO2
from decomposition
zygote
4. from earliest times human distributions have
been inextricably tied to plants
(embryo)
sporophyte
our preliminary knowledge about plants arose
from trial & error experiences
eg. hunter/gatherers: roots, berries, seeds
~8000BC agriculture – cereals
!greater yields and growth
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Plants: Introduction; Ziser Lecture Notes, 2010.8
only plants and fungi are primarily terrestrial
organisms
300-400BC: greeks –identification
by 200AD: Romans – crop rotation, manure, grafting,
plant varieties
eg. heart shaped leaves ! for heart ailments
today the science of plants continues as
botany with many specialties:
physiology
genetics
agriculture
!true plants probably arose ~465 MY (ordovician)
ago as green algae moved from water to
land
[photosynthetic bacteria began to colonize the land long
before algae or plants ~1.2 BY ago]
humans use plants for:
shelter,
furniture,
chemicals,
lubricant
latexes,
etc
! only a few are truly aquatic
! these two kingdoms have a long history of
symbiosis
by 1700’s: larger “herbals” folklore, medicinal
properties of plants
food,
heat,
antibiotics,
oils,
rubber,
poisons,
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Origins of Plants
our formal study of plants:
morphology
systematics
horticulture
Plants: Introduction; Ziser Lecture Notes, 2010.8
Advantages of moving from water to land:
clothing,
paper,
dyes,
waxes
resins,
1. plenty of light
2. CO2 more easily available than in water
3. no competition for minerals or growing space
(at first at least)
esthetic benefits
recreation (camping, backpacking, hiking)
house plants
flowers
Disadvantages of moving from water to land:
1. obtaining & holding onto water
water now becomes a limiting factor
need to find ways to get it and to store it
also outer surface must become more water tight
2. gas exchange
Plants: Introduction; Ziser Lecture Notes, 2010.8
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
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as outer surface becomes less permeable still need a way to
get gasses in and out
3. need effective support to counteract
counteract gravity
eg. resistant seeds, dormancy, evaporative cooling to
withstand environmental extremes
eg. specialized structures to get egg and sperm together
and to disperse offspring
most organisms in water are naturally buoyant or have
floats or gas sacs to lift them to the surface
all plants appear to have arisen from green algae
4. must be able to withstand greater extremes
in temperature, weather, etc
[probably charophytes are closest algal relative]
!must develop ways survive freezing, drought, extreme
heat, etc
Evidence for green algal ancestor to plants:
1. most green algae are found in freshwaters and
damp terrestrial habitats
5. reproduction and dispersal on land requires
some way to get sex cells together and some
way to disperse offspring
in water gametes and zygotes are released directly into the
water
many of the distinctive characteristics of plants
evolved to solve the problems for living on
land:
including swamps and marshes where some of the
earliest plant fossils first appear
primitive plants are still tied to water
2. many green algae today can live on land:
some are found in moist soil, forest floor and tree
trunks
eg. cellulose cell walls offered enough support for
living on land
3. some green algae produce larger multicellular
forms such as “seaweeds”
eg. plants developed vascular tissue to move water and
nutrients around and for added support
some of the earliest plant fossils resemble some of
these multicellular green algae
eg. plants developed roots to find water and
minerals
4. the cells of both green algae and plants:
eg. plants developed waxy cuticle to prevent water loss
Plants: Introduction; Ziser, Lecture Notes, 2010.3
eg. plants can store food in specialized structures such as
rhizomes, tubers, storage roots, etc
! main pigment is chlorophyll a
! store starch in plastids rather than free in cytoplasm
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Plant Cells
! have cellulose in cell wall
! have peroxisomes (contain protective enzymes)
! cytoplasm divides by cell plate
animals have 100’s of different kinds of cells
plants have relatively few kinds
plant cells share many features with most eukaryotic
cells:
nucleus
cell membrane
mitochondria for aerobic respiration
ribosomes for protein synthesis; but much fewer
compared to bacteria and animals
additional structures typical of most plant cells
a. cellulose cell wall – protection, support,
porous for moving things into and out of cell
b. plastids:
chloroplasts – contain chlorophyll for photosynthesis
chromoplasts – contain other pigments: fruits, flowers
amyloplasts – colorless, store starch
c. large central vacuole
other eukaryotes have various kinds of smaller vacuoles
but a larger vacuole is characteristic of plant cells
for storage & simple support
Plants: Introduction; Ziser, Lecture Notes, 2010.3
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
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Plant Tissues
wilting indicates that this vacuole requires addition
water
the cell is the basic structural and functional unit of
plants (all all life)
watering plant restores the ability of the vacuole to
support the plant cells
only one kind of plant cell, the sperm, is able to move
using a flagellum
each cell in plant requires a continuous supply of
water, oxygen, nutrients
in large plants it would be impossible for each cell to
“fend for itself”:
-light cannot penetrate to interior cells
-light cannot penetrate below ground
-water, nutrients and gasses are not easily accessible to
interior cells or those below ground
therefore, in multicelled organisms groups of cells
become specialized to perform a specific
function
eg. protection, photosynthesis, support, etc
!more efficient
!division of labor
!but all become dependent on each other
can no longer survive alone
tissues are groups of similar cells that have become
specialized for specific functions
There are 3 main kinds of plant tissues:
Plants: Introduction; Ziser, Lecture Notes, 2010.3
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b. periderm
1. Dermal Tissue
2. Vascular Tissue
3. Ground Tissue
!covers the stems and roots of perennial plants
a. epidermis
each plant organ (roots, stem, leaf) contains
all three tissues
usually a single layer of tightly packed cells
covers and protects the young plant
1. Dermal Tissues
generally no chloroplasts; cells are transparent
dermal tissue covers the entire outside of the
plant
allows light to penetrate into interior photosynthetic cells
on leaves and herbaceous stems, the epidermis:
is the “skin” of a plant
-secretes waxy protective cuticle to restrict
water loss
main functions of dermal tissue:
! physical protection
! thicker in drier habitats; thinner in wet habitats
! water conservation
and protect from pathogens and disease
! repairs damaged area
-contains pores (=stomata) for gas
exchange
! absorbs water and minerals
! contains pores for gas exchange
-epidermis of leaves & stems may contain
leaf hairs (= trichomes) with a variety of
functions
two kinds of dermal tissue in plants:
a. epidermis
! covers the leaves in all plants
! covers stems and roots in herbaceous plants (eg.
annuals and biennials)
Plants: Introduction; Ziser, Lecture Notes, 2010.3
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on roots, cells of the epidermis produce root
hairs
Plants: Introduction; Ziser, Lecture Notes, 2010.3
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!greatly increase the surface area of the
roots for absorption of water and mineral
!move water and minerals from roots to leaves
!move organic chemicals such as sugars and hormones
throughout the plant
b. periderm
! provide support for plant
periderm replaces epidermis in stems and
roots of woody plants
!provide cooling for plants in hot weather
two main kinds of vascular tissue:
forms the outer layer of “bark”
much thicker for better protection since plants
live many years
periderm consists mostly of dead cork cells
always found together in each plant organ
=vascular bundles
a. xylem:
cells contain suberin
made up of dead cells that are joined
together to form long hollow tubes that
branch throughout the plant
–a fatty material for waterproofing
instead of stomata, periderm often with
lenticels for gas exchange
generally larger cells with thicker cell walls
2. Vascular Tissue
moves water and minerals from roots, up the
stem to the leaves
the plumbing of vascular plants
consists of a series of interconnected tubes that
extend throughout the plant form tips of roots
to all leaves
main functions of vascular tissue:
Plants: Introduction; Ziser, Lecture Notes, 2010.3
xylem & phloem
b. phloem:
made up of living cells connected end on end
that branch throughout the plant
cells generally smaller with thinner cell walls
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b. pith
moves sugars, hormones and organic
materials throughout plant for use or
storage or signaling
ground tissue in the center of some stems and roots;
interior to the vascular bundles
c. mesophyll
3. Ground Tissues
ground tissue in the leaves that does photosynthesis
and gas exchange
this tissue forms the bulk of young plants, annual
plants and most leaves
Meristem Tissue
fills most of ‘space’ between dermal and
vascular tissues
in addition to the three basic kinds of tissues plants
also contain clumps of undifferentiated, embryonic
cells that can give rise to any of the other tissue
types
does most of the plants’ metabolic work
functions of ground tissue:
all plant cells arise from these embryonic plant
cells
=actively dividing cells
! photosynthesis
! food storage
meristem is located wherever growth is occuring
! some support in herbaceous plants or organs
! gas exchange
!in buds along the stems of plants
! secretion; some cells secrete: nectar, oils, mucilage,
resin
!in woody plants, as a layer of tissue called the
cambium that forms new vascular tissue and
periderm
referred to by different names in different
locations in plant:
a. cortex
the ground tissue in roots and stems between
epidermis and vascular bundles
Plants: Introduction; Ziser, Lecture Notes, 2010.3
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
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Plant Organs
Reproductive Organs
probably the most recognizable feature of plants are
their simple organs
unlike in most animals, plant reproductive organs
are always temporary structures
organ = groups of tissues arranged in clearly
defined structures or parts
some plants produce asexual reproductive organs
plant organs are much simpler than animal organs
all plants produce sexual reproductive organs
eg. capsule, sori
eg. antheridia, archegonia, sporangia, cones, flowers,
fruits.
each plant organ contains all three plant tissues
dermal, vascular & ground tissue
plants are classified based mainly on the kinds of reproductive organs
that they produce so these organs will be discussed when we
describe the major kinds of plants
two basic categories of plant organs
!vegetative & reproductive organs
a. Vegetative Organs
almost all plants have developed three major
vegetative organs:
a. an underground portion that anchors the plant and in
some absorbs water and nutrients
= root
b. some kind of supporting structure for the leaves
=stem
c. a flat structure used for most photosynthesis
=leaf
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
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[like hyphae of fungi]
Vegetative Plant Organs
taproots extend deep to water tables
Roots
shallow fibrous roots are better at collecting rainwater
normally found below ground
3. food or water storage
they are nonphotosynthetic and therefore not green
surplus carbohydrates produced by leaves are sent to roots for
storage
usually highly branched
some desert plants can store water in taproots
often more extensive than above ground part of plant
whatever conditions the above ground part of plant is subjected
to the roots most often survive
eg. corn roots: 8 ft deep, extends 4 ft in diameter
even in winter when whole above ground plant
dies back, roots live and resprout the next spring
eg. tamarisk (desert shrub): roots are up to 165’ deep
Root Structures:
eg. 4 month old ryegrass plant in one gallon of soil!had 310
miles of roots
A. patterns of root growth:
roots grow rapidly
1. taproots
up to 2” per day
1 main root with many smaller lateral
branches
soil conditions greatly affect extent of root growth
Root Functions:
eg. dandelion
1. Anchor plant
most mature trees begin with a taproot but at
maturity have large, shallow, lateral roots
instead
extend into soil
may be thick strong taproot or extensive spreading roots
but hickory retains its taproot
2. Gather water & minerals
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
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2. fibrous roots
epidermal cells behind root cap and growing
zone produce long threadlike extensions
=root hairs
several to many roots of same size that
develop from bottom end of stem
greatly increase surface area for absorption
! up to 90% of root absorption occurs
through root hairs
smaller lateral roots branch from them
eg. onions, crabgrass, monocots
3. adventitious roots
removing plant from soil destroys most of these root hairs
! decreases plants ability to absorb water
any roots that arise from other places on
stems or directly from leaves
! need to keep transplants moist
often modified for various additional functions
eg attachment, reproduction, etc
B. Parts of the Root
since plants lack any kind of respiratory system each
organ must be able to carry out gas exchange on
its own
like all plant organs roots need O2
1. root cap
good soil normally has lots of air spaces to
allow gas exchange with roots
tip of each growing root is protected by a
root cap
eg. wont grow well if covered by concrete
! covers and protects rapidly dividing cells of
root (apical meristem)
eg. soil with too much clay (Austin) must be aerated with
compost and sand for most plants to grow well
!also directs tip of growing root downward
eg. soil aerators sold at home stores
when cap is removed
! roots grow randomly until they
grow new root cap
a few plants that grow in stagnant water or
waterlogged soil produce pneumatophores
that act as siphons to draw air into the root
2. root hairs
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
Stems
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
at nodes are leaves, buds or branches
arrangement of buds and leaves on stem:
in plants with true stems, there is no sharp line of
demarcation between roots and stems
opposite
alternate
whorled
basal
the stem is typically above ground and the roots,
below ground
!
!
!
!
2/node
1/node
3 or more/ node
only around base of stem
new stems, leaves or reproductive organs develop
from buds
but many variations exist.
terminal bud = tip of stem
axillary bud = at nodes
General Stem Functions:
2. Stems can be herbaceous or woody:
1. Support
leaves and reproductive organs for maximum efficiency
a. herbaceous
2. Internal transport:
annual or biennial - grow 1 or 2 years then die
stems connect the nutrient and water gathering organs
(=roots) with the food synthesizing organs (=leaves)
dermal tissue is epidermis
Conducting water and minerals from the root to other parts
of the plant.
Conducting food, which is manufactured in the leaves by
photosynthesis, to all other parts of the plant
stem is usually green
b. woody stems:
the first land plants (465MY) were small herbaceous plants
that grew low to the ground
External Features of Stems
80 MY later (385 MY) we find the first fossils of trees; ie
woody plants indicating that plants had developed
vascular tissue and true roots, stems and leaves
and the strong supportive secondary growth that
allows trees and shrubs today to grow many feet high
1. leaves and buds branch off at specific locations on
the stem= nodes
distances between nodes = internodes
the first tree’s also led to a revolution in terrestrial ecology:
Plants: Introduction; Ziser, Lecture Notes, 2010.3
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-the roots dug into cracks and crevases speeding up
the weathering of rock and soil
-as trees decomposed they began to build rich humus
soil
-the leaves removed large amounts of CO2 from the
air and replaced it with large amounts of O2
hard, thick, long lived; stem is not green
may also have trichomes
2. Vascular Tissue
arranged as bundles of xylem and phloem just inside of the
epidermis
dermal tissue is periderm with cork
3. Ground Tissue
outer surface of periderm often contains
raised areas = lenticels for gas exchange
fills in the spaces between vascular tissue and epidermis
Anatomy of Woody Stems
bulk of stem consists of tough woody xylem
tissue
Plants that live more than one year, ie. perennials,
produce secondary growth each year.
!lots of cellulose and lignin
the stem grows in width from embryonic cells
(meristem) in a layer of cambium within
each vascular bundle
woody plants are either:
trees = branching relatively high above ground
each year this cambium produces new layers
of xylem and phloem cells.
shrubs = branches at or near ground
since woody stems are perennial: they maintain
some embryonic tissues that can grow into new plant
tissues and organs
xylem grows much faster than phloem
Anatomy of Herbaceous Stems
! virtually all of the “wood” of a tree is
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dead xylem cells
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vs lighter sapwood (still used for
transport)
the layers of phloem are much thinner and
become part of the bark
Dendrochronology
The phloem, on the “outer-side” of the cambium,
the cortex and the periderm make up the bark of
a tree.
growth rings can also retain info on yearly climate and other
factors that affect growth
! can date back to ~9000 yrs
Differences in the size of the xylem cells
produced throughout the growing season
produce the familiar “growth rings” in
the wood.
eg. Mesa verde
!Cliff Palace constructed in 1073
!Pueblo Bonito 919-1130
spring: fastest growth, plenty of water and nutrients
!cells are larger with thinner walls
=springwood
late summer: less water fewer nutrients available
!cells are small and thicker walled
= summerwood
wood is typically produced in the stem (=trunk) but
major roots of trees also usually have wood, bark
and annual rings
the arrangement of different cell types in the
secondary tissue results in the distinctive
characteristics of each kind of wood:
the oldest cells are closer to the center of the
trunk
eg oak, maple, pine, etc
the amount of old wood closest to the
center expands as new cells are laid
down in the vascular cambium
variations in wood structure:
1. in moist humid tropics trees do not produce
annual growth rings
!environmental conditions determine
the presence or absence of rings
these older cells are often darker and are
called heartwood.
xylem becomes plugged with pigments,
tannins, gums and resins
! heartwood no longer functions in transport
Plants: Introduction; Ziser, Lecture Notes, 2010.3
1. Epidermis on outside
outer surface has stomata in thin epidermis for gas exchange
woody stems are mainly the secondary growth
of perennial plants (grow >2 yrs)
Plants: Introduction; Ziser, Lecture Notes, 2010.3
soft and green
little or no woody tissue
usually short lived: characteristic of annual plants
little or no growth in diameter
eg. those growing in areas with pronounced
wet and dry seasons show rings
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but may be more than one ring per year
Leaves
2. in Panama canal zone is “the valley of square
trees”
leaves are the most variable part of a plant
a species of cottonwood
can be round, needle-like, scale-like, cylindrical,
heart-shaped, fan shaped
trunks are roughly square in cs;
an entire set of terminology is used to describe
growth rings are also square
shape
margins
vein patterns
ways of attaching to stem
believed to be due to local growing conditions
3. softwood vs hardwood
vary in size:
raffia palm ! 20 M (65’) long
duckweed ! 1/32nd of an inch
Victoria water lily pads up to 12’ circumference
pines and other conifers typically have
wood that lacks fibers and vessel
elements have only tracheids for
conduction
Function of Leaves:
! conifer woods are generally softer than
wood of flowering plants
1. Carry out most photosynthesis for most plants
herbaceous stems also do photosynthesis
2. Gas Exchange
hardwoods are mostly flowering plants
(dicots, except Balsa Ochroma
leaves have pores (=stomata) that
pyramidale))
!take in CO2 for photosynthesis
today >4500 products are made from wood
!release water vapor and O2
3. Absorption
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
all leaves can absorb some water and minerals
Plants: Introduction; Ziser, Lecture Notes, 2010.3
eg. most conifers, live oaks, privets, etc
deciduous ! tree loses all its leaves at the
same time
eg. miracle grow fertilizer is sprayed on leaves of many
yard plants, eg roses
in some plants leaves absorb most of the
nutrients and water
eg. in temperate areas – before winter
eg. epiphytes
helps them survive low temperatures of
winter
eg. pond plants
metabolism and photosynthesis slow
saves water
Leaf Structure
eg. in tropical areas – before dry periods
A. leaf arrangement on stem
opposite
alternate
whorled
basal
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!
!
!
!
eg. maples, most oaks, sumac, pecan, etc
2/node
1/node
3 or more/ node
only around base of stem
C. leaf anatomy
1. most leaves consist of two parts:
B. leaf permanence
petiole & blade
all trees (and other perennial plants) shed leaves
but not eg. grasses and other monocots
in perennial plants the leaves can be deciduous
or evergreen
petiole ! thin flexible stalk that allows blade to move
freely in the wind
in some plants the petiole can change orientation
of leaf to make photosynthesis more
efficient
evergreen ! tree loses leaves year round
but always has some leaves on the
tree
base of petiole often with 1 or 2 stipules and/or
an axillary bud
can be an advantage in areas with
short growing seasons
blade ! does most of the photosynthesis
usually thin, greatest exposure to the sun
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
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leaves tend to be arranged on tree and among
trees to provide greatest access to sunlight
vascular tissue can be seen as leaf veins
also help support the blade
! a single blade on a petiole
compound
!1 blade on a single petiole
b. leaf hairs (=trichomes)
outgrowths of epidermal cells
2. leaves can be simple or compound
simple
but some floating plants have them on the upper
surface
eg. some have protective function
eg. stinging nettle – contain poisons that inhibit
herbivory
eg. in some mountain wildflowers (eg. Edelweiss)
leaf hairs protect plants from intense UV
radiation
3. other parts of leaves
a. stomata
leaf epidermis contains pores (=stomata)
for gas exchange
stomata are protected by two guard
cells
stomata generally open during day, closed at night to
conserve water
in many desert plants, stomata are closed during
day and open at night
eg. many desert plants have a thick “furry” layer of
trichomes to reduce windspeed and reduce
water loss from pores
eg. in plants in salty environment often have
trichomes on leaves that remove excess salt
(excretion)
eg. may produce various volatile chemicals with
distinctive scents to ward off herbivores
unlike flower scents, leaft trichomes produce
aromatic products that are not released until leaf
is touched
4 main plant leaf scents (mainly terpenoids):
turpentine (pine needles)
camphoraceous (wormwood, yarrow, sage)
mint
miscellaneous (parsley,onions, watercress,
celery)
during drought, stomata may remain closed
during day
evaporation of water from stomata also helps to cool
plant in summer
usually more stomata on lower surface of leaf
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c.
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also, leaves of many grasses accumulate
silica
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Reproductive Plant Organs
sometimes forms teeth at edge of leaf that can
easily cut flesh
in addition to vegetative organs plants typically
produce reproductive organs
4. Leaf variations due to environmental
factors:
unlike most animals:
sexual organs are usually temporary structures
eg. plants in arid environments often have thick
leathery leaves with fewer pores to reduce water loss
appear as plant reaches maturity
eg. and may have dense hairs to reflect light and
keep plant cooler
in perennials, may form each year
eg. leaves that develop in shade are usually
thinner with fewer leaf hairs
eg. leaves that float on the surface of ponds have stomata
on top of leaf rather than on the bottom as in most
plants
reproductive organs can be produced for asexual
reproduction or sexual reproduction
organs for asexual reproduction
!produce asexual spores
capsule
sori
strobili (asexual cones)
organs for sexual reproduction
!produce egg and sperm
antheridium and archegonium
cones (sexual cones)
flowers and fruits
specific kinds of reproductive organs are characteristic
of each major plant group and will be discussed
with each group
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Plants: Introduction; Ziser, Lecture Notes, 2010.3
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Plant Diversity
General
Plants are classified into 4 major groups:
!from simplest to most complex
!from oldest to most recently evolved
Mosses
(~15,000 species)
small, simple, in moist habitats, oldest fossils
eg mosses, liverworts, hornworts
Ferns
(11,000 species)
more complex tissues and organs
eg horsetails, whisk ferns, club mosses
Seed Ferns (>>>1000; extinct)
Conifers (760 species)
mostly trees and shrubs, reproduction by producing
pollen, and seeds in “cones”
eg pines, spruce, fir, cedar, cypress
Flowering Plants
(235,000 species, 90% all plants)
most complex in terms of structure
reproduce by producing pollen, and seeds in fruits
eg. lilies, irises, grasses, wildflowers, crop plants,
oaks, willows, maples, etc
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