Page:First course in biology (IA firstcourseinbio00bailrich).pdf/81

 CHAPTER IX

THE STEM—KINDS AND FORMS; PRUNING

The Stem System.—The stem of a plant is the part that bears the buds, leaves, flowers, and fruits. Its office is to hold these parts up to the light and air; and through its tissues the various food-materials and the life-giving fluids are distributed to the growing and working parts.

The entire mass or fabric of stems of any plant is called its stem system. It comprises the trunk, branches, and twigs, but not the stalks of leaves and flowers that die and fall away. The stem system may be herbaceous or woody, annual, biennial, or perennial; and it may assume many sizes and shapes.

Stems are of Many Forms.—The general way in which a plant grows is called its habit. The habit is the appearance or general form. Its habit may be open or loose, dense, straight, crooked, compact, straggling, climbing, erect, weak, strong, and the like. The roots and leaves are the important functional or working parts; the stem merely connects them, and its form is exceedingly variable.

Kinds of Stems.—The stem may be so short as to be scarcely distinguishable. In such cases the crown of the plant—that part just at the surface of the ground—bears the leaves and flowers; but this crown is really a very short stem. The dandelion, Fig. 33, is an example. Such plants are often said to be stemless, however, in order to distinguish them from plants that have long or conspic