VEGETATIVE OEGAKS OF PLANTS. 291 



across, the fiber-like bundles of dnets and wood-cells are 

 seen disposed somewhat uniformly throughout the sec- 

 tion, though less abundantly towards the center. On 

 splitting the fresh stalk lengthwise, these vascular bun- 

 dles may be torn out like strings. At the nodes, where 

 the stem is branched, or where leaf-stalks are attached, 

 the vascular bundles likewise divide and form a net-work. 

 In a ripe maize-stalk which is exposed to circumstances 

 favoring decay, the soft cell-tissue first suffers change 

 and often quite disappears, leaving the firmer vascular 

 bundles unaltered in form. A portion of the base of 

 such a stalk, cut lengthwise, is represented in Fig. 47, 

 where the vascular bundles are seen arranged parallel to 

 each other in the internodes, and curiously interwoven 

 and branched at the nodes, both at those (« and fc) from 

 which roots issued, or at that (c) which was clasped by 

 the base of a leaf. 



The endogenous stem, as represented in the maize- 

 stalk, has no well-defined bark that admits of being 



Fis. 47. 



stripped off externally, and no separate central pith of 

 soft cell-tissue free from vascular bundles. It, like the 

 aerial portions of all flowering plants, is covered with a 

 skin, or epidermis, composed usually of one or several 

 layers of flattened cells, whose walls are thick, and far 

 less penetrable to fluid than the delicate texture of the 

 interior cell-tissue. The sbem is denser and harder at 

 the circumference than towards the center. This is due 

 to the fact that the bundles are more numerous and 

 older towards the outside of the stem. The newer bun- 

 dles, as they continually form at the base of the growing 

 terminal bud, pass to the inside of the stem, an'\ af^er- 



