GROWTH AND CELL DIVISION 



67 



The place where growth takes place varies in different organs. 

 In most leaves (Fig. 35) growth is uniform over the entire leaf 

 surface, although in the case of long, narrow leaves it may con- 

 tinue longer at the base than at the apex. In stems growth is 

 more localized than in leaves ; it continues for a longer period 

 and extends over a larger portion of the stem than it does in the 

 root tip just studied. In 

 herbaceous stems (Fig. 36) 

 growth may continue at 

 the apex of the main 

 shoot or its branches for 

 several weeks or for the 

 entire growing season, as 

 in the root. This growth, 

 like that of the root, is 

 due to an active meristem 

 at the stem tip, within 

 the apical buds, in which 

 active cell division fur- 

 nishes new cells for con- 

 tinuous growth in the 

 elongating zone, which, 

 as indicated above, may 

 extend over several-inter- 

 nodes at the apex of the 

 stem. 



FIG. 36. Growth in length of a root of corn 

 and of the stem of a bean seedling; 



The spread of the markings in b and d indicates 



the places of greatest growth. Observe the 



greater area over which growth takes place in 



the stem as compared with the root 



In woody stems growth 

 in length takes place in 

 terminal or in lateral buds, as in herbaceous stems. The buds 

 of woody stems, however, usually contain most or all of the 

 parts of the next season's shoot formed in advance, so that its 

 growth in the spring is completed more quickly than in herba- 

 ceous stems, and the plant is thus able to expand its leaves in 

 a comparatively short time when conditions favorable to spring 

 growth occur. In the lilac (Fig. 37) the bud a is composed of 

 the leaves of the next season, arranged on the very short axis of 

 the future branch. The internodes separating the successive 



