STRUCTURE.] 



EXOGENS PITH. 



185 



1. Of the Exogenous Structure. 



Fig. 33. 



The CELLULAR SYSTEM in an Exogenous stem chiefly occu- 

 pies the centre and the circumference, which are, however,, 

 connected by thin vertical plates of the same nature as them- 

 selves. The central part (a, fig. 34.) is the pith, that of the 



fig. 34. 



circumference (b) is the bark, and the connecting vertical 

 plates (c) are medullary rays. 



*Pith. 



The PITH is a cylindrical or angular column of cellular 

 tissue, arising at the point of separation between the root and 

 stem, and terminating at the leaf-buds, with all of which, 



