Trees in which the main trunk does not continue are said to be deliquescent. The branches arise from one common point or from each other. The stem is lost in the branches. The apple tree, plum (Fig.[ 58]), maple, elm, oak, China tree, are familiar examples. Deliquescent means dissolving or melting away.
| Fig. 57.—Excurrent Trunk. A pine. | Fig. 58.—Deliquescent Trunk of Plum Tree. |
Each kind of plant has its own peculiar habit or direction of growth. Spruces always grow to a single stem or trunk, pear trees are always deliquescent, morning-glories are always trailing or climbing, strawberries are always creeping. We do not know why each plant has its own habit, but the habit is in some way associated with the plant’s genealogy or with the way in which it has been obliged to live.
The stem may be simple or branched. A simple stem usually grows from the terminal bud, and side branches either do not start, or, if they start, they soon perish. Mulleins (Fig. [53]) are usually simple. So are palms.
Branched stems may be of very different habit and shape. Some stem systems are narrow and erect; these are said to be strict (Fig. [54]). Others are diffuse, open, branchy, twiggy.
Nodes and Internodes.—The parts of the stem at which buds grow are called nodes or joints and the spaces between the buds are internodes. The stem at nodes is usually enlarged, and the pith is usually interrupted. The distance between the nodes is influenced by the vigour of the plant: how?
Fig. 59.—Rhizome or Rootstock.
Stems vs. Roots.—Roots sometimes grow above ground (Chap. VII); so, also, stems sometimes grow underground, and they are then known as subterranean stems, rhizomes, or rootstocks (Fig. [59]).