VEGETATIVE ORGANS OP PLANTS. 



293 



The stems of the grasses are hollow, except at the 

 nodes. Those of the rushes have a central pith free from 

 vascular tissue. 



The Minute Structure of the Endogenous Stem 

 is exhibited in the accompanying cuts, which represent 

 highly magnified sections of a Vascular Bundle or fiber 

 from the maize-stalk. As before remarked, the stem is 

 composed of a groundwork of delicate cell-tissue, in 

 which bundles of vascular-tissue are distributed. Fig. 

 48 represents a cross section of one of these bundles, c, 

 g, h, as well as of a portion of the surrounding cell-tis- 



Fig. 49. 



sue, a, a. The latter consists of quite large cells, which 

 have between them considerable inter-cellular spaces, i. 

 The vascular bundle itself is composed externally of 

 narrow, thick-walled cells, of which those nearest the 

 exterior of the stem, h, are termed bast-cells, as they 

 correspond in character and position to the cells of the 

 bast or inner bark of our common trees ; those nearest 

 the center of the stem, c, are wood-cells. In the maize 

 stem, bast-cells and wood-cells are quite alike, and are 



