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 the leaves are the important functional or working parts; the stem merely connects them, and its form is exceedingly variable.
| Fig. 53.—Strict Simple Stem of Mullein. | Fig. 54.—Strict Upright Stem |
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 the 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 conspicuous stems. These so-called stemless plants die to the ground every year.
Fig. 55.—Trailing Stem of Wild Morning Glory (Convolvulus arvensis).
Stems are erect when they grow straight up (Figs. [53, 54]). They are trailing when they run along on the ground, as melon, wild morning-glory (Fig. [55]). They are creeping when they run on the ground and take root at places, as the strawberry. They are decumbent when they flop over to the ground. They are ascending when they lie mostly or in part on the ground but stand more or less upright at their ends; example, a tomato. They are climbing when they cling to other objects for support (Figs. [36],[ 56]).
Fig. 56.—A Climbing Plant (a twiner).
Trees in which the main trunk or the “leader” continues to grow from its tip are said to be excurrent in growth. The branches are borne along the sides of the trunk, as in common pines (Fig. [57]) and spruces. Excurrent means running out or running up.