NATURE OF PLANTS 



83 



effected by the formation of new cells at the apex of the stem. 

 Fig. 61 shows the general features to be noticed in the tip of 

 a stem as seen in longitudinal section. New cells are being 

 formed at the apex by division just as in the case of the root. 

 Below this formative region is the zone of elongation in which 

 the cells gradually change in character so that the cortical and 



Fig. 62. Diagram of the tip of a stem as seen in longitudinal section : 

 a, formative region corresponding to the part shown in Fig. 61 ; I, b, leaves 

 and branches in various stages of development ; v, vascular bundles ; c, 

 cortex; p, pith. 



central regions are apparent and in certain elongated cells we 

 note the first indication of the vascular bundles (Fig. 61, x). 

 The leaves also originate in this region through the active divi- 

 sion of the superficial cells of the stem. The branches of the 

 stem develop somewhat later in the axils of the leaves, and more 



