378 



MANUAL OP BOTANY 



some few Dicotyledons it is many-layered. It is absent from the 

 roots of Equisetum. Its cells are parenchymatous ; it does not 

 show so mtioh differentiation as it does in the stem, rarely con- 

 taining, when more than one layer of cells thick, any additional 

 form of tissue except secretory ducts. When thickening of the 

 roots occurs it gives rise to certain merismatio layers which 



Fig. 766. 



Fig. 766. Section of stele of root. After Kny. en. Endodermis. pe. Peri- 

 cycle, x. Xylem bundles, the protoxylem, :t„ abutting on the perlcycle. 

 ph. Phloem bundles alternating with the bundles of xylem. p. Pith, or 

 conjunctive tissue of the stele. 



take an important share in the process. The vascular bundles 

 vary in number, but the bast and the wood are never conjoined ; 

 they lie side by side with each other, on separate radii of the axis 

 with a little conjunctive tissue between them. They are first 

 noticeable as procambium strands, and gradually take on the 

 forna of their permanent tissue. In the differentiation of the 



