LABORATORY
EXERCISE #10
KINGDOM
PLANTAE
Introduction
Vascular
plants
include most of the plant species with which we are familiar. The plants which make up a majority of our
food, the forest trees from which our dwellings are made, the plants which
furnish the fibers of which our clothes are constructed, all are vascular
plants. So also are the shrubs, which
surround our homes, the delicate flowers that brighten our lives, and the logs
crackling in the fireplace. The
distinguishing characteristic of this group is its possession of vascular tissue. This tissue serves the plants in much the
same way as the animal circulatory system, delivering materials from one part
of the plant to another.
The two types of vascular tissue found in plants
differ in appearance and function. The xylem (pronounced "zy lum") conducts water and dissolved minerals
from the sites of their absorption in the roots, to the remainder of the
plant. It also aids in the mechanical support of the plant. Phloem
("flow um"), on the other hand,
moves food materials from the site of formation or storage, to other parts
of the plant.
ACTIVITIES
a.
Select a slide marked "Dicot
and Monocot Root", examine under low power and find the specimen that
resembles the photographs of Figures 75a and c in your Photo Atlas. Focus on the
circle of cells in the center and locate the xylem and phloem. The large, thick-walled xylem vessels
usually take on a red stain, while the thin-walled phloem cells are
greenish-blue.
Diversity
Among The Vascular Plants
There
are three major groups of vascular plants.
1. The primitive
vascular plants, which do not form seeds, include the ferns, club mosses and horsetails. These taxa have life cycles in which the sporophyte generation is predominant,
unlike the mosses studied previously.
The gametophyte generation, though diminutive, is none-the-less free living. Like the mosses, these plants
reproduce by the use of spores, rather than seeds. All three groups have
long fossil histories and once dominated the land. Those species existing today hang on in rather specialized
ecological niches.
ACTIVITIES
b.
Consider the herbarium specimens of the ferns. These plants
typically have an underground stem
with many small, wiry roots and comparatively large leaves or
fronds. Aided by Atlas Figures
51a and b, examine the fronds and look for brownish spots on the underside of
some leaflets. These are the fruit dots and bear the spores; consequently, this plant is a
sporophyte. Note the diversity in size
and shape among the ferns.
c.
Select a slide of the fern
prothallus (gametophyte). This
tiny, heart-shaped organism is shown in Figure 53a. It bears the male reproductive structures (antheridia), as well as the female organs (archegonia). Also present
on the prothallus are tiny, root-like rhizoids. Locate all these structures, using Figures
53a and b to assist you.
d.
Examine the herbarium specimens of
club mosses and compare them to the photographs in Figures 48a-c in your Photo Atlas. These are the last of a proud group, which dominated the forests
of the earth during the Carboniferous Period, some 350 million years ago. Those ancestral club mosses were large
trees, up to 150 feet high. Much of the
coal mined today was formed from the remains of these swamp-dwelling
plants. A fossil club moss is available for your examination.
e.
Also inhabiting those Carboniferous swamps were large, leafless plants
ten meters high and as big around as a man's thigh. The descendants of those organisms are the horsetails. Only one genus
and about a half dozen species exist today, but they are never the less
interesting plants. Look at the
herbarium specimen and/or plastomounts of horsetails, as well as the
photographs on page 50 of Perry and Morton.
The leaves have been reduced
to whorls of scales and the green stem has taken over the job of
photosynthesis. The epidermis of these
plants contains high levels of silica, a rough and abrasive mineral, leading to
their being used as scouring pads by pioneer women.
2. The gymnosperms
are primitive seed plants which are present in abundance today and which are
very important to modern humans. The
cone-bearing trees (conifers) are a
part of this group. They include the
oldest, tallest and bulkiest living organisms (bristle-cone pines, redwoods and
sequoias, respectively). Most of the
timber used in building construction comes from such conifers as pine, fir,
cedar and redwood, and we enjoy using the beautiful evergreen gymnosperms for
ornamental plantings.
The sporophyte generation dominates the gymnosperm life cycle; indeed,
the gametophyte has been reduced to only a few cells and there are two types,
male and female, both of which usually form on the same tree. Seeds which are not formed inside a fruit
also bring about reproduction. The name
gymnosperm means "naked seed,"
a reference to the small seeds of the conifers which lie naked upon the scales
of the reproductive structure or cone.
All gymnosperms are woody plants. In addition to the conifers, the cycads (Figure 54a and b) and ginkgos
(Figures 54c and d) make up the group.
ACTIVITIES
f.
Examine the herbarium mounts of conifers. Note the woody stems, the needle-like or scale-like leaves and the cones. Remember, this is part of a sporophyte.
g.
Look at the representative cones
presented. Do you suppose there is a
direct correlation between the size of the tree and the size of its cones? Actually there is not.
3. The angiosperms
are the flowering plants. The reproductive structure of the angiosperm
is the flower and the seeds are
protected by the thickened wall of the ovary, within which they form and
mature. This "ripened" ovary,
with its seeds, is termed a fruit. The angiosperms include large forest trees
with their woody supporting stems, as well as the smaller herbaceous plants which lack wood.
It is difficult to
over-emphasize the importance of angiosperms in today's world. Most of the mid-latitude and tropical
forests are made up almost exclusively of "hardwood"
trees which belong to this group.
Basically all of the plant materials we eat and/or feed to domestic
animals are the products of angiosperms.
Most birds, mammals and insects find home and sustenance among these
plants, and we enjoy the sight and smell of their flowers and languor in their
shade. Can you imagine a world without
this group of plants?
The angiosperms are divided
into two major groups, based on a few easily-identified characteristics. Illustrated in Figure 22.9, p. 381 in Starr,
these are:
A. The monocots are all
herbaceous. Their flower parts are in
threes or multiples of three, and a
cross-section of the stem reveals
scattered bundles of vascular tissue.
The leaves of monocots have the vascular tissue confined to many parallel veins. Included in this group are the lilies, the
orchids and the grasses.
B. The dicots may be
herbaceous or woody. Their flower parts
are in fours or fives or multiples
of these. Their vascular bundles are arranged in a ring, and the
veins of the leaves form a network. All of the hardwood trees are dicots, as are
many crop plants such as beans, tomatoes, cabbage, etc., and a majority of the
spring flowers.
Angiosperms may complete an entire life cycle in one
year, over-wintering as seed (annual
plants), or they may live for many years (perennials). Some woody
angiosperms are evergreen (southern
magnolia, for instance), while others are deciduous,
losing all their leaves in the Fall and replacing them in Spring.
ACTIVITIES
h.
Examine any live specimens of
angiosperms. Note the division of
the plant body into roots, stem and leaves. If flowers are present, note their
location. Using the criteria listed
above, and assisted by Photo Atlas Figures
59a and b, can you identify the plant as a monocot
or dicot? Is it woody or herbaceous?
i.
Examine the herbarium specimens
of monocots. Are they woody or
herbaceous? Note the parallel veins of the leaves.
j.
Look at the preserved specimens
of dicots. Are they herbaceous or
woody? Compare the net-veined leaves seen here with the parallel veins of the
monocots.
The
Vascular Plant Body
The typical vascular plant is made up of the roots, stems and leaves (See Figure
22.2, p. 378 in Starr). There are many
modifications of these basic parts and the varying combinations give rise to
the infinite variety which exists in the plant kingdom. The remainder of this laboratory period is
given to examining some of this variety.
1. The
roots typically constitute that part of the plant which lies below ground
level. The roots' primary functions are
to anchor the plant in its
substrate, absorb water and mineral
nutrients from the soil and store
food materials. Toward those ends,
plants have evolved two types of root systems, both of which are illustrated in
Figure 22.15 on page 386 of Starr. In
some plants, the grasses for example, the root system consists of a tangle of
many equal-sized parts. These are
termed fibrous roots. Others, like the carrot, have a single
dominant root which grows straight down from the stem. While there may be several smaller roots as
well, this tap root dominates.
ACTIVITIES
k.
Look at the plastomounts illustrating root types. Be able to
distinguish between fibrous roots
and tap roots.
l.
Examine a slide of root hairs. Using Figure 74a in Perry and Morton, locate
the root cap. This mass of cells protects the growing tip
of the root by lubricating its passage through the soil and by sacrificing its
own cells to save the delicate tissue behind it. Some distance behind the root cap you may observe the stubs of root hairs which are out growths from
some epidermal cells. It is in the root
hair region that most water and minerals are absorbed by the root.
ACTIVITIES
m. Examine one of the twigs presented and, using Figures 78c
and d in your Photo Atlas, identify
the terminal bud, lateral buds, and leaf scars. The scars left
by past years' terminal buds are visible as rings around the twig and are
termed nodes. The space between two
nodes represents one year's growth. How
many years growth can you count on the twig you are examining?
n.
Select a slide of Monocot and
Dicot stems. Use the
photomicrographs on page 77 in Perry and Morton to help you identify which is
which. In the monocot (probably corn)
the vascular bundles are more or less scattered around the periphery of the
stem. Note the "monkey face"
look of the vascular bundles, owing to the large xylem vessels. The dicot stems, on the other hand, lack the
"monkey face" in the vascular bundles, which are arranged in a
definite ring around a large mass of pith.
3. On most
plants, parts of the shoot have been expanded and flattened into special photosynthetic organs called leaves. Some leaves may be thickened to also serve as a site for storage of food and/or water, and others may be modified to protect the plant, as in the case of cactus spines. The leaf is divided into a stem and the
expanded, flattened portion; the blade.
The veins of the blade
contain the vascular tissues. While the
leaves of angiosperms are flattened, those of gymnosperms are typically divided
into thin needles.
ACTIVITIES
o. Examine the herbarium specimens
showing the leaves of both angiosperms
and gymnosperms. Can you tell the
difference? Aided by Starr Figure 22.11
(p. 382), be able to differentiate between
simple and compound leaves. Your
instructor will assist you.