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1
Chapter 2
STRUCTURE OF HIGHER
PLANTS
Gymnosperms and angiosperms
Gymnosperms have “naked seed”
 Most gymnosperms are narrow-leaved evergreen
trees like pines, spruces and firs
 http://nature.snr.uvm.edu/www/mac/plantid/gymnosperms/gymnosperms.html


Angiosperms have seeds enclosed within an
ovary
 Most angiosperms are broad-leaved flowering
plants
2
Monocots and dicots


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Monocots or monocotyledonous plants have
an embryo with only one seed leaf.
Other characteristics of monocots are:
1) Parallel veins
2) Diffuse vascular bundles
3) Flower parts usually in multiples of
three.
Monocot stem
Dicots


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Dicots or dicotyledonous plants have
embryos with 2 seed leaves.
Other characteristics of dicots are:
1) Leaves have net shaped venation
2) Vascular bundles are distributed around a
central vascular cambium
3) Flower parts are usually in multiples of
four or five
Dicot stem
From:http://www2.cdepot.net/~walser/worldofscience/Biology/Pictorial%20Help/Botany/mo
ocots_dicots.htm
From: http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookPLANTANATII.html
Monocot
germinationCorn
Dicot germination- Bean
Major parts of the plant cell

The protoplast includes:
•
•
•
•

plasma membrane
the cytoplasm
the nucleus
the vacuole
Plasma membrane = plasmalemma
• a double membrane, actually a lipid bilayer,
surrounding the cytoplasm and cell organelles.
Major parts of the plant cell


The cytoplasm = thick liquid within the
plasmalemma containing endoplasmic
reticulum and plastids of various types.
The endoplasmic reticulum = membranes
where proteins are synthesized on
ribosomes.
Major parts of the plant cell



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Plastids = capsule-like organelles bound by
a double membrane.
Plastid types:
Chromoplasts - contain pigments like
chlorophyll (chloroplasts) and several
others.
Leucoplasts - colorless and serve as storage
bodies for oil, starch and proteins.
Major parts of the plant cell


Mitochondria - smaller than plastids,
double membrane bound.
“Powerhouse” of the cell - involved in
respiration and ATP production.
• ATP-an energy rich compound.

Mitochondria -also involved in protein
synthesis.
Major parts of the plant cell


The nucleus =the organelle which contains
chromosomes; long lengths of DNA
containing the genetic code.
Vacuoles - surrounded by a membrane
called the tonoplast.
• Vacuoles serve as storage for the cell.
• Vacuoles also regulate turgor (keep cells
“inflated”)
Major parts of the plant cell

The primary cell wall - composed mainly of
cellulose, pectic substances and lingins.
• provides protection for the protoplast and structure for
the plant.

The middle lamella -lies between adjacent cells
holding them together.
 The secondary cell wall - lies inside the primary
wall and is composed of cellulose, lignins,
suberins and cutins.
Major parts of the plant cell



Plasmodesmata - strands of cytoplasmic
tissue connecting individual cells to each
other.
http://www.cellsalive.com/cells/plntcell.htm
http://koning.ecsu.ctstateu.edu/cell/cell.html
Plant tissues



Plant tissues = large tracts of organized
cells of similar structure that perform a
collective function.
Meristematic tissue or meristem =
actively dividing cells which can
differentiate into other tissues and organs.
Permanent tissues= fully differentiated
tissues developed from meristems.
Meristematic Tissues

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
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Apical meristems:
1) shoot apical meristemsDetermine leaf patterns and branching habit opposite, alternate, spiral
Produce primary vascular tissues and stem
tissue
May produce terminal flowers or remain
vegetative and continue to grow producing
flowers on lateral growth depending on the
plant
Meristematic Tissues

2) root meristems-

Found at the root tips
Some plants have a dominant taproot which
develops mainly downward with little
lateral growth.

• Examples include: carrots, beets, oaks and
pecans.
Meristematic Tissues

Many plants lack a strong tap root and so
they develop a well branched fibrous root
system.
• Grasses, grains and shallow rooted trees are
examples.

http://koning.ecsu.ctstateu.edu/Plant_Biolog
y/meristems.html
Subapical meristems

Subapical meristem -produces new cells a
few millimeters behind an active apical
meristem. Cells also expand in this area
increasing internode length.
• Plants that bolt like mustard, and lettuce do so
because of the activity of the subapical
meristem.
Intercalary meristems

Intercalary meristems = meristems
separated from other meristematic tissues
by older more mature or developed tissue.
• Intercalary meristems are located just above the
leaf sheath of grasses and many other
monocots.
From:
http://www.puc.edu/Faculty/Gilbert_Muth/art0
037.jpg
Lateral meristems


Lateral meristems = cylinders of actively
dividing cells somewhat below the apical or
subapical meristem continuing through the
plant axis and producing secondary growth.
May be referred to as vascular cambium
• produces new xylem and phloem tissue;
• the cork cambium produces mainly bark.
Lateral meristems

The continued increase in diameter of trees
and other woody perennials -> lateral
meristems.
• The “growth rings” that are produced in woody
plants which allow determination of plant age
are created by this lateral growth.
Woody Stem Cross Section
Insert
drawing from
page 21
:
From: Champion
Paper Co.
Permanent tissues

Simple tissues = permanent tissue
composed of only one cell type.
• Examples : epidermis, collenchyma,
parenchyma, sclerenchyma and cork.

Complex tissues -composed of of more
than one cell type.
• Examples are xylem and phloem.
Simple tissues

The epidermis = single exterior layer of cells that
protects plant parts.
• The epidermis is often covered with cutin, a waxy
substance that prevents water loss.

Parenchyma tissue -made of living thin walled
cells with large vacuoles and flattened sides.
• Parenchyma cells retain the ability to become
meristematic and can heal wounds and regenerate other
types of tissues.
Simple tissues

Sclerynchyma tissue - composed of thick walled
cells found throughout the plant as fibers and
sclerids.
• The protoplasts in these cells die eventually.
Sclerynchyma cells are common in bark, stems and nut
shells.

Collenchyma tissue- gives support to young
petioles, stems and veins of leaves.
• Cell walls of collenchyma are thickened cells mainly
made up of cellulose.
• A living tissue
Simple tissues

Cork tissue occurs mainly in the bark,
stems, and trunks of trees.
• The cell walls are suberized (suberin is a waxy
substance), and the protoplasts are short lived.
• As a result cork tissue is mostly dead.
Complex tissues

Xylem = a complex tissue that conducts
water and dissolved minerals in plants.
• Xylem can be composed of vessels, tracheids,
fibers and parenchyma.

Vessels = long tubes made up of short
vessel members .
Complex tissues


Tracheids =long, tapered dead cells that
conduct water through pits.
Fibers = thick walled sclerenchyma cells
that provide support to plants.
• Most xylem tissue is missing one or two of
these cell types.
Xylem
From:
http://www.iacr.bbsrc.ac.uk/n
otebook/courses/guide/xylem.
htm
Complex tissues

Phloem -a complex tissue which conducts
metabolites (food) from the leaves to stems,
flowers, roots and storage organs.
• comprised of sieve tubes, sieve tube members,
companion cells, fibers and parenchyma.
Phloem

Sieve tube members = long slender cells
with porous ends called sieve plates and are
found only in angiosperms.
• Gymnosperms have sieve cells which are
similar but lack the sieve plate.

Companion cells -closely associated with
sieve tube members and aid in metabolite
conduction.
Phloem

Phloem fibers - thick walled cells that
provide stem support.
• Parenchyma cells in the phloem serve as
storage sites.
Phloem
THE PLANT BODY

Roots• conduct water and mineral nutrients
• support and anchor the plant
• May serve as storage organs for
photosynthesized food.
THE PLANT BODY

The root cap - a layer of cells that covers
the root tip and protects the procambium as
the root pushes through the soil.
• Cells of the root cap are continually sloughed
off and replaced by new cells to keep the
protective layer intact.
Root cross section
From:
http://www.puc.edu/Faculty/Gilbert_Muth/phot0027.jpg
More roots…….

The endodermis = a single cell layer found
only in the root.
• Each cell in the layer is encircled by a
waterproof band called the Casparian strip
which does not let water and nutrients between
the cells.

In order for the soil solution to get in to the
xylem it must travel through the cell itself
(protoplasm).
Casparian strip
And still more roots...

The procambium layer produces :
 A) The pericycle - the outermost layer of the cells
found just inside the endodermis.
• The pericycle is the area where lateral roots are formed
and in some instances the vascular and cork cambium
are produced here.

B) The vascular cambium also produces primary
xylem and phloem,and in some plants pith.
Adventitious roots

Roots arising from any location other than
the primary root (radicle) = adventitious
roots.
• Adventitious root formation is the basis for
producing many new plants from cuttings .
Stems

From the outside in:
 Epidermis - a single layer of cells which is
usually cutinized to keep it from drying out.
• Stomata are also in this layer to allow for gas exchange.

The cortex lies just inside the epidermis and is
made up of collenchyma, parenchyma,
sclerenchyma, and secretory cells.
Stems continued...

Collenchyma cells lie just below the epidermis and
add strength to the stem.
 Sclerenchyma cells serve a similar purpose.
 Parenchyma cells may continue to divide and and
form new tissue to heal the stem if it is wounded.
 Primary phloem is the next layer in dicots
followed by the procambium, xylem and pith.
Stems continued...
From: http://www.ualr.edu/~botany/monocotstem.jpg
Woody dicot stem
Early wood vs. late wood
Herbaceous
Dicot Stem
Herbaceous
Monocot Stem
Leaves
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Monocot - parallel veins.
Dicot - veins organized in a net like pattern.
Leaves primary function is photosynthesis.
Leaves secondary function is transpiration.
Leaf structure

Epidermis is present on the upper and
lower leaf surfaces.
• usually covered with a waxy cuticle to prevent
tissue desiccation.
• Hairs may also be present on the surface to
reduce wind velocity and create a boundary
layer.
Leaf structure

Guard cells =specialized cells which occur
in pairs forming stomata which open and
close allowing for gas exchange and
transpiration.
• Stomata are more abundant on the lower leaf
surface in most plants.
Guard cells
Leaf structure


Transpiration = the loss of water from the
plant which helps to regulate leaf
temperature.
The palisade and spongy mesophyll layers
contain chlorophyll for photosynthesis.
Leaf structure


The palisade layer of parenchyma cells
lies directly below the epidermis
The spongy mesophyll layer of
parenchyma cells lies directly below the
palisade layer and contains spaces which
allow for gas movement.
Buds

A bud is generally defined as an undeveloped
shoot or flower composed mainly of meristematic
tissue.
 Buds may be :
• 1)vegetative- producing shoots
• 2) flower
• 3) mixed- producing both shoots and flowers.

Adventitious buds are buds arising in places buds
don’t normally form.
• This allows for propagation by root cuttings in some
plants like sumac.
Flowers and flower structure

Angiosperms
• specialized leaves born on and arranged on the stem
adapted for sexual reproduction = flowers.

Inflorescences = more than one flower attached to
the same stalk.
 Flowers may be at the top of the stem or in the
axils of the leaves farther down the stem.
 Flowers can be very useful in plant ID.
Flowers and flower structure

Complete flowers have four parts:
•
•
•
•
sepals
petals
stamens
pistil(s)
Flowers and flower structure

Sepals are the leaf like scales that encircle
the other flower parts.
• Sepals are usually green, but may also be
colored.

All the sepals together on the flower are
termed the calyx.
Flowers and flower structure

Petals are the next whorl of leaves in from
the sepals.
• Petals are usually brightly colored and often
contain nectaries which secrete nectar and
attract insects.
Flowers and flower structure


The term for all the petals together is
corolla.
The corolla and the calyx together are
called the perianth.
Flowers and flower structure

The next whorl of parts found inward from the
petals are the male flower parts known as the
stamens.
 Each stamen consists of the filament and anther.
• The filament is a stalk-like structure supporting the
anther.
• The anther produces pollen.

All the stamens together in the flower form the
androecium.
Flowers and flower structure


The pistil is the female flower structure.
The three parts of the pistil are:
• 1) stigma- the receptive “sticky” end that
receives the pollen
• 2) style- the tube connected to the stigma;
• 3) ovary- the flask shaped structure at the base
of the style.
FROM:
http://www.csdl.tamu.edu/FLORA/301Manhart/repro/Flo
wer%20diagram/flower_diagram.htm
Floral Structure
From:http://www.biologie.unihamburg.de/b-online/e02/02d.htm
Flowers and flower structure


Incomplete flowers are flowers that lack
one or more of the four parts (sepals,
petals, stamens, or pistils.)
Flowers that lack stamens but have pistils
are termed pistillate flowers.
Flowers and flower structure


Similarly, flowers that lack pistils but have
stamens are termed staminate flowers.
Imperfect flowers lack either male
(stamens) or female (pistils) flower parts.

Both staminate and pistillate flowers are
imperfect flowers.
Flowers and flower structure

Plants with staminate and pistillate flowers
on the same plant are known as
monoecious.
• Corn is an example of a monoecious plant.
Flowers and flower structure

Plants with staminate and pistillate flowers
on the different plants are known as
dioecious.
Buffalograss
-dioecious
Fruits


A Fruit is a matured ovary and its associated
parts.
Most fruits bear seeds, except for those
termed parthenocarpic fruits like seedless
oranges.
Fruits


The pericarp or ovary wall can develop
into peels, shells or even the fleshy part of
fruit depending on the plant.
http://www.ibiblio.org/botnet/glossary/a_xi.
html
Fruits

Simple fruits are fruits which are formed
from a single ovary from one flower.
Fruits



Most commonly simple fruits are classified
as fleshy, semi-fleshy or dry depending on
the texture of the mature pericarp.
Aggregate or multiple fruits are formed
from several ovaries.
The true fruit is attached to or contained
within a receptacle or accessory structure.
Fruits



Aggregate fruits are formed from one
flower with many pistils on the same
receptacle, strawberries are an example.
Multiple fruits are formed from many
flowers that occur in cluster, pineapples are
an example.
http://www.orst.edu/extension/mg/botany/fr
uit.html
Seeds

A seed is a mature ovule with three basic
parts:
• the embryo
• the food storage tissue (endosperm, cotyledons
or perisperm)
• seed coats (also known as testa)
Seeds

The embryo is a plantlet formed within the
seed during fertilization.
• The embryo has two growing points the
radicle, which is the embryonic root and the
plumule (or coleoptile) which is the embryonic
shoot.
• One or two cotyledons (seed leaves) are
located between the radicle and plumule.
Seeds



Albuminous seeds store most of their food
in the endosperm.
Exalbuminous seeds store most of their
food in fleshy cotyledons (like the bean), or
occasionally in the perisperm.
Food reserves are in the form of starch, fat,
or protein.
Seeds


Seed coats also known as testa are
generally tough to protect the embryo. They
are formed from the integuments which are
the outer layers of the ovule.
The hilum is a scar left on the seed where it
was attached to the stalk.
Seeds


The micropyle is a small opening near the
hilum.
The raphe is the ridge on the seed.
Seed parts
Presentation adapted from :
Hartman,
et al 1988. Plant Science,
Second Edition, Englewood Cliffs, N.J.:
Prentice- Hall.