THE PLANT BODY 



79 



and, just within, the cortex made up of several layers of cells. 

 Still further toward the center of the root, the central cylinder 

 appears, which shows differentiating vascular bundles. 



Passing now to a point a little above, we find the growth 

 zone merging imperceptibly into a region in which many of the 



c 



FIG. 43. Cell division and tissue differentiation in a growing root tip. Dia- 

 gram of root (a) shaded to show the several regions from which the highly mag- 

 nified sections (6, c, d, d', e) are taken. (From Densmore.) 



epidermal cells on the outer surface of the root are modified 

 into BOOT HAIRS. It has been emphasized above that the 

 primary function of the root is the intake of certain of the 

 elements of food in solution. This function is performed 

 almost entirely by osmosis through the extensive area af- 

 forded by the surface of the root hairs, and accordingly cells 



