CH. Ill] 



ROOT-TIP. 



41 



as bricks put on raise a wall by a single course only. But 

 this would be quite wrong ; each cell that has been created 

 by cell -division at the growing point undergoes great 

 increase in size before it becomes a permanent member 

 of the root. 



The root of the bean is not so easily understood or 

 so instructive as that of the maize, and the drawing 

 (fig. 16) which illustrates root -structure is therefore taken 

 from that plant. 



FIG. 16. 

 DIAGRAM ILLUSTRATING THE STRUCTURE OF THE ROOT-TIP IN 



LONGITUDINAL SECTION. 

 . c, cortex. v.c, central cylinder. r.c, root-cap. 



The points to notice are (1) the central cylinder cc 

 seen in longitudinal section, ending a dome-like mass of 

 meristem. Then (2) the cortex which thins away to a layer 

 of meristem only one cell thick, which keeps forming 

 new cortex cells. Then (3) the sharply marked root-cap ro 

 whose new cells are made by another layer of meristem. 



