138 



A TEXTBOOK OF BOTANY 



[Cn. IV, 4 



ing deeply buried under the bark, and yet finally give origin 

 to branches. 



Where the terminal bud is notably prominent, as in Horse 

 Chestnut (Fig. 75), the axillary buds are largest just below 

 it, and progressively smaller farther back. Such a terminal 

 bud unfolds its flowers, stem, and foliage very quickly and 

 makes no more growth in length that season, though the upper 

 axillary buds may develop into branches. Such is DEFINITE 

 ANNUAL GROWTH. Where the terminal bud is relatively small, 

 as in Elm, it continues to grow and produce new leaves and 

 axillary buds all summer, and new branching takes place from 

 the lower new buds. Such is INDEFINITE ANNUAL GROWTH. 



The occurrence of a bud in the axil of every leaf gives the 

 plant a great surplus, of which few ever develop into branches, 

 though all are capable of so doing. Generally speaking, 

 those nearer the outer ends of the branches, and therefore 



nearest the light 

 and free space, 

 are the ones 

 which develop, 

 though if the ter- 

 minal, or outer 

 axillary, buds be- 

 come destroyed, 

 whether by frost, 

 insect ravage, or 

 experimental de- 

 sign, the next 

 lower develop in 

 their places. 

 Since all are 

 capable of de- 

 velopment, it is evident that some factor controls them 

 collectively, either inhibiting the development of some or 

 stimulating that of others, a subject to which we shall 

 later return under Growth. 



FIG. 92. A bud, of unusually elongated form, 

 of a water weed, Elodea canadensis, in exterior view 

 and section, showing the development of leaves; 

 X 150. (After L. Kny.) 



