=741. Bud-scars, and how to tell the age of the plant.=—In general the bud-scales when they fall away in the spring leave scars termed scale-scars, and the whole aggregate of scale-scars makes up the bud-scar. The position of the buds of previous winters is, therefore, marked. It becomes an easy matter to determine the age of a branch, since all that is necessary is to follow back from one bud-scar to another, the portion of the stem between representing, except in rare cases, one year’s growth. A woody plant grows in height only by the formation of new sections of stem added to the apex or side of similar sections produced the previous season, never, as is commonly supposed, by the further elongation of the previous year’s growth. Hence a branch once formed upon a tree is fixed as regards its distance from the ground. The apparent rise of the branches away from the ground in forest trees is an illusion caused by the dying away of the lower branches. =742. Definite and indefinite growth.=—With the opening of the buds in spring, growth begins. In some cases, when all the members for the season were formed, but still minute, within the bud, such growth consists solely in the expansion of parts already formed; in others only a few members are thus present to expand, while new ones are produced by the growing point as the season progresses. In most cases growth is completed by the middle of July, soon after which buds are formed for next year’s growth. Such a method of growth is termed definite. In a few woody plants, as, for example, sumach, locust, and raspberry, growth continues until late in the autumn. In such cases the most recently formed nodes and internodes are unable to become sufficiently “hardened” before winter sets in, and are killed back more or less. Next season’s shoot is a branch from some axillary bud. Such growth is termed indefinite. [Illustration: Fig. 432. Three-year-old twig of the American ash, with sections of each year’s growth showing annual rings.] =743. Structure of woody stems.=—If we make a cross-section of a woody twig three general regions are presented to view. On the outside is the rather soft, often greenish “bark,” so called, made up of sieve tubes, ordinary parenchyma cells, and in many cases long fibrous cells composing the “fibrous bark.” From a growing layer in this region, termed the phellogen, the true corky bark of the older trunk is formed.