Plant Morphology

During this laboratory period, you will examine the external morphology of a typical representative of the Anthophyta (the flowering plants), the most prominent group of plants today. You will become familiar with the various parts of the plant body. You will also start plants growing which will be used in later laboratory exercises.

I. SEEDS

Examine the bean seeds which have been soaking overnight. The outer layer is the SEED COAT. The scar, or HILUM, indicating the place of attachment of the seed to the wall of the fruit, is readily visible. Close to one end of it is a small pore, the MICROPYLE. Remove the seed coat and carefully note the relation of the hilum and micropyle to the parts of the EMBRYO within. The bean embryo consists of two large fleshy COTYLEDONS attached to the short AXIS. Above the point of attachment of the cotyledons is the PLUMULE or EPICOTYL, below the attachment is the HYPOCOTYL. The latter terminates with the embryonic root, called the RADICLE. Scrape the inner surface of one of the cotyledons, and add a drop of I2KI (5 g I2 + 10 g KI / 100 ml dH2O). If starch (an insoluble carbohydrate commonly stored in plants) is present, it will stain blue-black.
    What do your results indicate about the function of the cotyledons?
Observe the cotyledons of bean seedlings.
    What other function is served by cotyledons in this species?

II. PLANT MORPHOLOGY

A "TYPICAL" HERBACEOUS DICOTYLEDONOUS PLANT. Study the bean plants (Phaseolus) of various ages which are available in the laboratory. Notice that there is a pale, non-green part which is normally subterranean--the root, and a green aerial portion--the shoot.

A. The Stem. The shoot system of a plant consists of a main stem and lateral branches, both bearing LEAVES. The leaves are attached at definite places on the stem called NODES. The interval of a stem between two successive nodes is an INTERNODE.
    Where on the plant are the nodes farther apart?
    Why do you think this occurs?
    Where on the plant is the diameter of the internodes the greatest?
    Why do you think this is so?
The angle between a leaf and the stem on which it is borne is called the LEAF AXIL. Look carefully at the axil and locate the AXILLARY BUD which occurs there.
    What structure arises from an axillary bud?
One of the stem's most important functions is to support the display of leaves and flowers (reproductive organs), but it also conducts water and dissolved minerals from the roots to the upper parts and food from the leaves to other portions of the plant.
    What is the color of the young stem?
    What additional function does this suggest for this portion of the stem?
Take the cut-off shoot and stand it in a small beaker of 1% Eosin Y. After several minutes observe the stem and leaves of the shoot.
    What function do the results suggest for stems?

B. The Leaf. A complete leaf may consist of three parts: a stalk or PETIOLE attaching the leaf to the stem, a thin expanded portion--the BLADE, and a pair of variously sized and shaped STIPULES at either side of the petiole where it joins the stem. Stipules are missing in many species. The petiole may be lacking, in which case the leaf is said to be sessile. A leaf in which the blade is not divided into segments, even though it may be lobed or toothed, is called a SIMPLE leaf. If it is divided into segments, or LEAFLETS, the leaf is COMPOUND. To distinguish between a compound leaf and a branch with several leaves, you must locate the axillary bud or buds which will occur in the axil of a leaf but not in the axil of a leaflet.
    What parts does the bean leaf have?
    Is the leaf simple or compound, or can both types be found?
Leaves may be arranged in one of three ways on the stem. If two leaves occur at the same node, the arrangement is OPPOSITE; if a single leaf is present at a node, it is ALTERNATE; and when three or more leaves arise at a node, the arrangement is WHORLED.
    What is the arrangement in bean?
If you hold a leaf blade up to a strong light, numerous lighter-colored lines may be seen. These are the VEINS. Re-examine the leaf veins on the shoot that was in the red dye.
    What do the results suggest as a function for the veins?
Notice how thick the major veins are by examining the underside of the leaf.
    What does this suggest as an additional function for veins?
There are three main patterns of VENATION in leaves although only two are common in angiosperms. If the veins run essentially parallel with one another, the leaf is PARALLEL-VEINED; if the veins branch freely in all directions to form a network, the leaf is NET-VEINED; if the veins fork regularly into two essentially equal parts, the venation is DICHOTOMOUS.
    What type of venation occurs in the bean leaf?

C. The Root. Observe the region where the stem and root merge.
    Is there a clear-cut line separating the root from shoot?
A transition region usually occurs at or near the ground level. Look closely at the root system of the plant. Does it have a single, large, tapering root extending downward from the base of the stem (a TAPROOT or PRIMARY ROOT) with smaller, tapering, SECONDARY or LATERAL roots branching from it, or does it have many roots, all about the same size, growing from the base of the stem to form a FIBROUS ROOT system?
In many root systems of the fibrous type, it is possible to identify, at least in the seedling stages, the root (primary) which is the direct continuation of the stem; it may have some short lateral branches. The other roots, equal in size to or larger than the primary, arise from the lower part of the stem and are ADVENTITIOUS.
    Do roots have nodes and internodes?
    Are the lateral roots aligned one above the other?
    Are the roots at one level aligned at 90 or 120 degrees apart?
    What are the functions of the root system?

Prepare a 1-page abstract and attach fully-labeled diagrams as evidence of your efforts in plant morphology.

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