Stems and twigs vary from the finest, lightest sprays to the most coarsely moulded ones,—from the delicate twigs of the hop hornbeam to the stout shoots of the horsechestnut;—like larger branches their tips either ascend, droop, or grow at right angles from the stem, and may be smooth, downy, or rough to the touch.
The pith in cross sections of twigs shows different forms and is a means in itself of distinguishing some trees. It is usually circular, but in some species it takes the form of a pentagon or a star. In a vertical section we sometimes find it in horizontal plates, like the chambered pith of the walnuts. The color is usually white, but sometimes we find it pink, yellowish, green, red, and brown.
It is interesting to find that the history of a tree for several years past can be told by studying the scars along the bare stems. The annual growth each year is marked by a circle of scars around the stem, which was left by the scales of the buds when they opened in the spring, and these scars mark each season’s growth for successive years along the stem.
Leaf-scars
Besides these circles of scars, there are scars on each side of the stem which were left by the leaves when they fell in the autumn. These leaf-scars differ distinctly in various species and may be round, narrow, triangular, oval, heart-shaped, or horseshoe-shaped according to the species of the tree. They are either flat upon the stem or on a projection, they are sometimes concave and again convex. They may be opposite each other on the stem, as those of the horsechestnut, maples, and ashes, or the arrangement may be alternate, as that of hickories, walnuts and oaks. The places on the stem where the leaf-scars appear are called nodes, and the spaces between the nodes are called internodes.
Occasionally stipule scars are found on the stems,—inconspicuous scars left by stipules, the leaf-like bodies found at the base of leafstalks on some trees,—and sometimes we find the scars of fruit stalks.
Bundle-scars
BUNDLE-SCARS
Bundle-scars are the scars of the little fibres, the vascular bundles which fastened the leaves to the stems in summer. They are found on the leaf-scars and usually take their shape more or less. On the large leaf-scars they can be seen clearly, but on delicate twigs where the leaf-scars are small it is well to use a magnifying glass.