46 MORPHOLOGY OF STEMS. 



79. While the root normally gives birth to no other organs, 

 but itself performs those functions which pertain to the relations 

 of the vegetable with the soil, binding it to the earth and 

 absorbing nourishing materials from it, the aerial functions of 

 vegetation are chief!}' carried on, not so much by the stem it- 

 self as by a distinct set of organs which it bears, name!}*, the 

 leaves. Hence, the production of leaves is one of the charac- 

 teristics of the stem. These are produced only at certain definite 

 and symmetrically arranged points, called nodes. (13, 23.) 



80. Development and Structure. In a bud or undeveloped stem, 

 the nodes are in contact or close proximity. In the develop- 

 ment, growth in length takes place in such manner as to carry 

 these apart more or less, according to the degree of elongation, 

 that is, the internodes (13) elongate. The order of development 

 is from below upward, the lowest internode first lengthening, 

 the others in regular succession. Each completes its growth, 

 with more or less rapidly, although the length attained varies 

 greatly in different stems, in different parts of the same stem, 

 and under different conditions. Unlike the root, in which the 

 elongation of formed parts is very soon finished and therefore 

 only the tip is perceptibly growing, internodes go on growing 

 throughout, and several formed internodes may be growing 

 simultaneously, thus producing elongation throughout a consid- 

 erable extent of stem and with considerable rapidity. But each 

 internode grows independently. Some parts of an internode 

 may lengthen faster or continue in growth longer than others ; 

 this is usually the upper portion, at least in long internodes and 

 when every part is equally exposed to light. 



81. The development of a stem from a bud is wholly like that 

 from the embryo, and has already been described in Chap. II. 

 It exhibits similar variations as to rapidity and vigor, dependent 

 upon the constitution of the bud, which, like the plumule in 

 the seed or seedling, may be either latent or much developed 

 before growth begins, also upon the amount of nourishment 

 provided. Strong buds commonly have their parts, or some of 

 them, ready formed in miniature, and a store of elaborated nour- 

 ishment in the parent stem to draw upon. Those well-developed 

 buds which in many of our shrubs and trees crown the apex or 

 occupy the axils of stem and branches early in the preceding 

 summer (as in Magnolia, Fig. 81, Horsechestnut, Fig. 85, and 

 Hickory, Fig. 91) often exhibit the whole plan and amount of 

 the next year's growth ; the nodes, the leaA r es they bear, and 

 sometimes the blossoms being already formed, and only requiring 

 the elongation of the internodes for their full expansion. As 



