THE ROOTS 



43 



The piliferous layer, when traced to the root apex, is seen to be the 

 outermost layer of the periblem. Near the tip its cells have thick mucil- 

 aginous walls (Fig. 31). 



FIG. 33- Transverse section showing the origin of a lateral root (/>') from the pericycle/) 

 ( x 385). e, Endodermis ; b, phloem. 



Adjacent to the initial cells of the periblem is the meristem of the 

 root - cap. As growth 

 proceeds, the outer cells 

 of the root-cap separate 

 from each other along 

 the middle lamella and 

 are rubbed off by friction 

 with the soil, through 

 which the roots extend, 

 the loss being made good 

 by division of the meri- 

 stem within. The ex- 

 foliated cells, at the time 

 of their separation, are 

 more or less turgid, and FIG. 34. Transverse section of a root showing a lateral 

 contain well-defined root (w) ' devel P in s PP site the P hloem < x 2I )- 

 nuclei and vacuolated cytoplasm (Fig. 32). 



Lateral rootlets are derived from the cells of the pericycle opposite 

 the phloem of the vascular cylinder, and not from points opposite the 

 xylem as in the roots of many plants (Figs. 33, 34). 



