ORIGIN OF THE ROOT-CAP 



01 



of the root proper to form a common initial zone: the rows of cells 

 which make up this common zone are, on the one hand, continuous with 

 the several component shells of the root-cap, and on the other penetrate 

 more or less deeply into the root proper. In extreme cases this joint 



Fro. -.'0. 



Longitudinal section through the root-apex of Pimm sativum. J. Common initial 

 zone ; c, its protodermal continuation ; p-p, central cylinder (plerome) ; r-T, cortex 

 (periblem). From de Bary, Comparative Anatomy. 



meristem produces, not only the cortex, hut also the central core (com- 

 prising both periblem and plerome) of the root. The protoderm, which 

 extends forward as far as the common zone of meristem, also continually 

 cuts off layers towards the outside which help to regenerate the root- 

 cap (Fig. 20). The roots of Pimm,, Vicia, Cytisus, Acer, Lavatera, 

 Foenicaluiit, etc., belong to this category. 



