Chapter
12
Botany- the study of plants
One reason the study of botany is so important to man is because all the
food eaten by man comes directly or indirectly from green plants.
About 2/3 of the food we eat comes directly from plants and 1/3 comes
from animals which eat plants.
Ways plants are beneficial:
1) Provide most of man's food
2) Release O2 needed by man and animals.
3) Plants are raw materials for many manufactured goods (paper, gum, wax, cloth, alcohol)
4) Plants are a source of beauty.
Misconceptions regarding plants:
1. All green things are plants.
May be algae, protozoan, bacteria, or fungus.
2. All plants are green.
Some have other pigments, which mask the chlorophyll.
3. All plants are autotrophic.
Some plants are heterotrophic (mistletoe, dodder, Indian
pipes; see page 289)
Divided into 9 phyla (often called “divisions”) (see pages 655-657) based on the presence or absence of vascular tissue (specialized structures that conduct H2O and dissolved materials in a plant)and seeds.
A.
Non-vascular plants
Phylum Bryophyta- plants without vascular tissues
Examples: mosses & similar plants such as liverworts & hornworts
B.
Vascular plants without seeds
Contains 4 phyla: (see page 293)
Phylum Psilophyta (whiskferns)
wiskferns: rare and unusual plants which lack true roots and
leaves
Phylum Lycophyta (Ground pines)
club mosses (also called "ground pine" because they grow along
the ground in temperate regions)
Phylum Sphenophyta (Horsetails)
horsetails: all but one group have become extinct
the epidermis contains a glasslike substance
(silica) which feels very rough to the touch.
Called "scouring rushes" - used for scouring pots
and pans before scouring powder and pads were known.
Phylum Pterophyta (Ferns)
C.
Vascular plants with seeds
Contains 4 phyla: Phylum Coniferophyta (cone-bearing plants)
Phylum Cycadophyta (mostly extinct; cycads)
Phylum Ginkgophyta (Ginkgo)
Phylum Anthophyta (angiosperms)
Class Mondoctyledoneae
Class Dicotyledoneae
PHYLUM BRYOPHYTA
Non-Vascular Plants
The Mosses and Similar plants
Bryophyta means "mosslike plant"
appears as a thick, velvety green carpet on moist rocks, trees, and ground made up of individual moss plants (2 types see pg. 290)
Not really moss: Irish moss (alga)
Reindeer moss (lichen)
Spanish moss (flowering plant)
Parts
of a moss plants:
leafy shoot- a slender stalk with leaflike structures
each of the tiny leaflike structures on moss is 1
cell layer thick
(generally less than 1 inch although in some tropical
species it may exceed 2 feet in length)
lack a protective cuticle so they can dry out easily
rhizoids- tiny hairless threads which grows into the soil to
absorb water and minerals
used for anchorage
not roots- lack conditioning tissue
Life Cycle of a moss: page 290
Involves both asexual and sexual reproduction
This marvelous process is known as the Alternation of Generations
The 2 generations are
(1) the sporophyte - produces spores Asexual
(2) the gametophyte - produces gametes Sexual
1) the top of the male gametophyte bears the Antheridia which
produces sperm
2) the top of the female gametophyte has 1 or more Archegonia
which contains the ovum
the slender neck of the archegonium is closed until the ovum is
ready to be fertilized
3) Sperm swim from the antheridia to the ova and fertilize the
ovum (zygote)
when water touches the top of the antheridium, the sperm are
released
4) Zygote grows into a stalk with a capsule which produces spores
5) When mature the cap comes off the capsule and the wind
distributes the spores
6) Spore grows when environmental conditions are right
7) First grows into a cellular filament called a protonema
8) Protonema then forms the leafy shoots and rhizoids
The dominant generation is the gametophyte generation (because it is more often seen)
Liverworts
The name "liverwort" dates from the 9th century. Means "liver plant"(see p. 4 & 5 Doctrine of Signatures)
Marchantia - a common liverwort with a Y-shaped thallus. Have
splash platforms which look like little umbrellas
(see p. 291)
Benefits of mosses:
1. Help to replenish the soil.
Secrets acids which gradually break down the minerals in
rocks (chemical weathering)
2. Help prevent soil erosion.
3. Peat (main constituent is peat moss or Sphagnum)
Dried peat is used as fuel in Iceland and other northern
regions.
Gardeners use peat moss to pack plants for shipment and
to mix with soil as fertilizer.
4. Has been used for surgical dressing (because of its
superior absorptive quality)
Vascular Plants Without Seeds
Phylum Pterophyta
The Ferns
Ferns are nonflowering vascular plants with spore-bearing leaves and horizontal underground stems.
Most are only 1 or 2 feet tall
Some tree ferns in tropical regions grow as tall as 60 feet and have leaves 12-14 feet long.
Some ferns are epiphytes (plants that grow on other plants but are not parasitic).
parts of a fern:
Fronds - the large leaves
Rhizome – a creeping or underground stem, which produces roots
Sori - groups of spore-bearing sporangia that appear as
brownish dots on the underside of fern fronds
(singular - sorus)
They are dense clusters of minute sporangia, each of
which contains between 48 and 64 microscopic spores.
sori - Greek "a heap"
The Fern Life Cycle (page 292)
Asexual (sporophyte) and sexual (gametophyte) - Alternation of Generations
A new fern's life cycle typically begins in July when the brownish sori appear on the undersurface or along the margins of the sporophytes' fronds (known as fertile fronds).
Sori may be round, kidney-shaped, oblong, linear, curved, or star-shaped.
Asexual:
1. Sori appear on the underside of a frond.
2. Sori first open and discharge millions of spores.
Sexual:
3. Spore develops into a tiny green, heart-shaped structure called a prothallus.
Quite different from the original fern plant and is
seldom seen (only 1 cell layer in thickness).
4. The underside of the prothallus develops archegonia and antheridia.
Archegonia - at the notched end of the prothallus(ova)
Antheridia - near the point of the "heart" (sperm)
5. Sperm are released from the antheridia and swim to the
ovum at the bottom of the archegonia.
6. Zygote matures and sends the first leaf up and the first root down
The first leaf of a fern is often a fan-shaped blade.
The second leaf is usually a fiddlehead, a coiled young
leaf. In some ferns fiddleheads are edible and used in
salads.
It usually requires between 3 and 7 years to reach reproductive maturity. Fern plants (sporophytes) live for several years and produce new fronds each year. Prothellia (gametophytes) only live 3 to 7 weeks, in which time they produce the archegonia and antheridia.
Dominant generation - sporophyte
Vascular
Plants With Seeds
Divided into two groups
A. gymnosperms (with 3 phyla)
B. angiosperms (with 1 phylum)
gymnosperms - the seed plants that do not first produce a flower before the seed; means "naked seed" - produce seeds not covered by the walls of an ovary.
See diagram on page 295.
Do not form flowers or fruits.
Produce cones or cone-like structures.
Phylum Coniferophyta
often called gymnosperms
Conifer refers to the cones.
All conifers produce seeds in cones.
Produce two types of cones (usually produced on separate shoots of the same tree)
1. Staminate cones: the pollen-producing cones
small, green, and inconspicuous
near the tips of the branches
shed after the pollen season is over
2. Ovulate cones: the seed-producing cones
large in comparison to staminate cones
range in size from less than 1" to more
than 2' in length
woody structures consisting of layers of
cone scales
seeds develop between the cone scales
seeds are generally winged because they
depend upon the wind for dispersion
"The geometry of the cone functions like a wind turbin,
channeling pollen around it in a way that maximizes
pollination - so that if pollen fails to land on one
scale, it is passed on to the next."
Life Cycle of a Pine Tree (page 296)
1. tree produces cones
2. pollen is carried by the wind from staminate cones to
ovulate cones
3. pollen lands on the open scales of the ovulate cone
4. the scales then close tightly (in many pines the cone begins
to point downward)
5. ovum is fertilized
6. when seeds are mature and environmental conditions are right:
scales open and release the seeds
Some noteworthy conifers:
Douglas fir - one of the biggest trees in western U.S. and
Canada; reaching a height of almost 300 ft.;
provide more than 1/4 of the timber cut in the
U.S. for construction
Sequoia - in central Calif.
some are among the oldest living things on earth
(2,000 - 3,500 years)
273 feet tall; 84 feet circumference; bark 1 ft. thick
Bristlecone Pines - of Calif. White Mountains
the oldest living things on earth
(more than 4,000 years old)
"they were already seedlings when Abram
left Ur of the Chaldees to go to the
Promise Land"
Coast Redwood - redwood trees are the tallest living things
on earth
some grow more than 350 feet tall
Phylum Anthophyta
The Flowering Plants
often called angiosperms
All have seed enclosed in an ovary(mature ovary is called a fruit)
All have flowers (not all are colorful blossoms - corn tassels and catkins of oak trees)
Two classes:
1. Monocotyledoneae - monocots (example – corn; daylilies)
2. Dicotyledoneae - dicots (example – peanut; lima bean;
columbines)
How monocots differ from dicots:
1. basic difference is the number of cotyledons in the
seed
cotyledon - "seed leaf"; a seed leaf in a plant embryo
that contains stored food
monocot - 1
dicot - 2
See and know chart on page 322
2. Number of leaves the embryonic plant has
monocot - 1
dicot - 2
3. Venation - the pattern of veins (fibrovascular bundles)
in a leaf
monocot - parallel leaf venation (veins in leaves start
at stem and go to the tip of the leaf)
dicot - netted leaf venation (continually branch)
4. Floral parts
monocot - floral parts in 3's or 6's
dicot - floral parts in 4's or 5's or multiples of 4 or
5
5. Roots
monocot - roots usually fibrous
dicot - roots usually are a tap root
Classification of plants according to their growth cycle:
(1) Annual - a plant which develops from a seed and produces
new seeds in a single growing season.
(they complete their entire life cycle in one
growing season)
examples: peas, beans, grains, zinnias,
pansies, marigolds
(2) Biennial - a plant that lives through two growing
seasons to complete its life cycle
examples: beets, cabbage, turnips, carrots,
foxglove, sweet william
(much of the time, biennials are harvested
after the first year, and thus we do not see
their flowers)
(3) Perennials - plants which live from year to year and
bloom each season
A. Herbaceous - soft-stemmed
examples: asparagus, wild flowers,
peonies, tulips, irises,
gladioli
B. Woody - examples: trees and shurbs
Plant Organs
Two groups:
A. Vegetative organs
leaves, roots, and stems
B. Reproductive organs
flowers, fruits, and seeds
Technically:
leaves, roots, and stems are vegetables
peas and corn are really seeds
eggplants and tomatoes are really fruits
green beans are fruits and seeds
Plant Tissues
tissue - a group of similar cells working together to perform a
particular function
Our bodies have four basic kinds of tissues: epithelial (skin)
muscle
connective
nerve
A typical plant has 3 distinct kinds of tissue: (see chart on p 300)
(1) Structural tissue
most of the body, or structure, of the plant is
structural tissue
produce food, store food, cover, support, and protect plant
examples: epidermis, parenchyma, mesophyll, collenchyma,
cork, sclerenchyma
(2) Meristematic tissue
purpose - the growth and repair of plants and plant
parts (where mitosis is occurring)
found in growing areas (buds, tips of roots and stems)
examples: apical and lateral meristem; vascular cambium, cork cambium, pericycle
(3) Vascular tissue
the plant's sap-conducting tissues (compared in some
ways with our circulatory system)
two types:
A. Xylem - transports water and dissolved
minerals (one kind of sap) upward
long, thick-walled cells
B. Phloem - transports food manufactured in the
leaves (the other kind of sap)
downward
Structures of a typical leaf
blade: the flat, green portion of a leaf
petiole: the stalk of a leaf that attaches it to the plant stem
Leaves which lack a petiole are referred to as sessil
leaves. (grasses and certain other monocots have sessile
leaves that attach to the stem by way of a sheath that seems
to wrap around the stem)
margin: the edge of a leaf's blade
veins: the pipelines that carry food and water throughout the
blade
stipule: a small leaflike or scalelike structure on a plant that
helps to cover a leaf while it is developing
Leaf Mosaic
leaf mosaic - the arrangement of leaves on a stem
types of leaf mosaic:
1. spiral mosaic - a series of single leaves arranged in a
spiral on the stem
2. alternate mosaic - leaves alternate from opposite sides
of the stem
3. opposite mosaic - two leaves grow from the same point on
the stem
4. whorled mosaic - three or more leaves grow from a single
point on a stem
Leaf Margins
margin: the edge of a leaf's blade
Types: (see page 301)
entire
undulate
serrate
dentate
Leaf Shapes
Types: (see page 302)
linear
cordate (heart shaped)
deltoid (triangular)
lobed
circular
Leaf Venation
venation: the pattern of the veins within leaves
two basic patterns of leaf venation:
(1) Parallel venation: a series of veins which originate
at the stem and proceeds to the tip
of the leaf (roughly in a parallel
fashion)
occurs in monocots - corn, grass,
irises, orchids
(2) Netted venation: large veins branch to form a network
of smaller veins throughout the leaf
occurs in dicots
A. Pinnate: if the veins branch off one large central
vein called a midrib
example - oaks, apple trees, african
violets
B. Palmate: if there are two or more main veins
coming from a single point
example - maples, ivy, geraniums
Leaves may be classified as either simple or compound
simple leaves - have one blade on every petiole
compound leaves - have more than one blade on every petiole
each small blade on a compound leaf is
referred to as a leaflet
example - pecan
The Covering of a Leaf
epidermis: the top and bottom layer
one cell layer in thickness
lacks chlorophyll
serves as protection
often secrets a waxy substance that forms a cuticle
usually transparent
some epidermal cells produce epidermal hairs
lower epidermis: tiny openings called stomata (stoma, sing.)(or
leaf pores) permit the exchange of gases between
atmosphere and spaces in leaf
main purpose - to allow air to move in and out of the
leaves
may be very abundant (apple tree leaf - 47,000 stomata
per square inch; oak tree - 100,000)
guard cells - two crescent-shaped cells around each
stomata; open and close the stomata (p 302)
The Inside of the Leaf
Between the upper and lower epidermis is the mesophyll.
It is in the mesophyll that most of the photosynthesis takes place.
It is structural tissue (called parenchyma)
Mesophyll is divided into two layers:
(1) Palisade Mesophyll
located toward the upper side of the leaf
consists of elongated, columnlike cells
there may be several layers of palisade mesophyll
abundance of chloroplasts which move in a circle
(2) Spongy Mesophyll
located toward the lower side of the leaf (sometimes
sandwhiched in the middle)
consists of large, irregularly shaped cells separated
by large air spaces
the air spaces form a system of passages throughout the
leaf that permits air to come in contact with the
individual cells
Veins
run through the mesophyll
contain the vascular tissue (xylem and phloem)
the large veins of a leaf contain thick-walled strengthening
collenchyma tissues around the vascular tissues
Falling Leaves
evergreen trees - retain their leaves thoughout the winter
deciduous trees - lose their leaves each fall and are bare all
winter
The major reason why plants lose their leaves in winter is that the lengths of the day and night change with the season, signaling the plant to prepare for harsh conditions. The leaves fall because they are actually "cut" from the stem by an abscission layer.
Read page 304
The Color of Leaves - Plant Pigments
Plant pigments:
1. Chlorophyll - green
different concentrations can produce various shades of
green
2. Xanthophyll (zan' tho fil) - yellowish colors
3. Carotene - yellowish-orange colors
both xanthophyll and carotene are Carotenoids (vitamin
A)
4. Anthocyanin (an' tho si' a nin) - red, blue, and purple
Read page 304
Leaf Modifications (page 307)
Some leaves have special functions, and thus their structure may be so different from ordinary leaves that we may not recognize them as leaves at all.
A special leaf is called a "modified leaf"
Modified leaf - one which has a special design for a special task
1. tendrils - special leaves of vines which have the unique
function of holding the vine upright by
coiling around some support structure
often extensions of the midribs of compound
leaves (as in the pea)
2. spines - special leaves which have no chlorophyll
3. succulent - store water
often the venation is completely hidden
4. aquatic leaves - enlarged spongy parenchyma (holds large
quantities of air); stored air causes
leaves to float
5. bracts - brightly colored leaves on plants that appear
to be showy flowers
Roots
Roots are the organs of the root system.
Functions of a root:
1. anchors the plant
2. absorbs water and dissolved minerals
3. transports absorbed substances
4. stores food (carrots, radishes, beets)
Roots systems are of two basic designs: (page 305)
1. Taproots - commonly found in dicots
- pentrates the soil with very little branching
often stores food (fleshy roots)
2. Fibrous - commonly found in monocots
- have no main section but branch out into the
soil in all directions
Root Structure
Root cap – dead, thick-walled cells; for protection
Epidermis - outer covering for protection
Root Hairs - long, fingerlike projections of root's epidermal cells that greatly increase the root's water-
absorbing surface area
Root Cortex - a region of a root below the epidermis where food stored
Vascular Cylinder - the control area of the young root (contains
xylem and phloem); the central area
Pericycle - a layer of meristenatic tissue in a root; the tissue
from which secondary roots arise
Vascular Cambium - this meristematic tissue can produce additional xylem and phloem
Stems
Major functions of stems:
1)manufacture, support, and display leaves
2)conduct materials
Branching Patterns
Three types of stem growth (see page 310):
(1) excurrent growth: trees with strong terminal buds on
(branching) the main vertical stem
grow tall and straight
branches coming from a large central
shaft
examples - pines, firs, hemlocks,
redwoods, cypresses
(2) deliquescent growth: trees with strong lateral buds
(branching) develop several main branches
examples - willows, cottonwoods,
elms
(3) columnar growth: crown of leaves on top
unbranched stem
example - palm trees
External design of a dormant twig: (see page 311)
Buds - the parts of the stem, which allows it to grow in
length or develop new stems, flowers or leaves
Terminal Bud or Apical (ap Y kal) bud - large bud at
the end of the twig
cause the stem to grow in length
Lateral Bud or Axillary buds - located along the sides
of the twig
purpose: to allow growth of new stems out from
the sides of the main stem
Bud scales - protect the tiny leaves in the dormant bud
Bud-scale scars - markings left by bud scales
indicate where last year's growth started
Nodes - place on stem where leaves are produced
Leaf scars - where petiole of a leaf was attached to stem
Internode - section between two nodes
Bundle scars - (in the leaf scar) tiny dots where xylem and
phloem went from stem to petiole
Lenticels - tiny openings in stem for gas exchange (means of
respiration)
Woody Stem Parts
Kinds of Wood