1

Chapter 2

STRUCTURE OF HIGHER PLANTS

2

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/plant-id/gym

nosperms/gymnosperms.html

Angiosperms have seeds enclosed within an ovary

Most angiosperms are broad-leaved flowering plants

Monocots and dicots

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 stemMonocot stem

Dicots

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 stemDicot stem

From:http://www2.cdepot.net/~walser/worldofscience/Biology/Pictorial%20Help/Botany/monocots_dicots.htm

From:http://www2.cdepot.net/~walser/worldofscience/Biology/Pictorial%20Help/Botany/monocots_dicots.htm

From: http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookPLANTANATII.htmlFrom: http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookPLANTANATII.html

Monocot germination- Corn

Monocot germination- Corn

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

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

Apical meristems: 1) shoot apical meristems- Determine 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_Biology/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/art0037.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 :

Insert drawing from page 21 :

From: Champion Paper Co.

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/notebook/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 Dicot Stem

Herbaceous Monocot Stem

Herbaceous Monocot Stem

Leaves

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/Flower%20diagram/flower_diagram.htm

Floral Structure

From:http://www.biologie.uni-hamburg.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/fruit.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.