THE MATERIAL OUTGO OF PLANTS 



343 



connected series, extending from the root-hair region to the mesophyll of 

 the leaves, among which they branch so extensively that there is scarcely 

 a cell which is separated from a strand by more than a half dozen of 

 its neighbors. 

 Here the first 

 branches end 

 blindly (fig. 

 638) or join 

 their fellows. A 

 section of the 

 root in the root- 

 hair region 

 shows likewise 

 that only a few 



FIG. 638. -Ending of a xylcm strand among the cells of the 

 mesophyll in a leaf of lilac (Syringa vulgaris) : t, tracheid ; i t in- 

 tercellular space. 



cells intervene 



between the free surface and the young xylem strands, which, nearer 



the root tip, are being differentiated from the plerome (p. 239). Like- 



FlG. 639. Skeletonized edge of a leaf of a Fieus, showing the mode of branching of 

 the smaller ribs ; the smallest are completely gone. From a photograph by LAND. 



wise, a section of the leaf (fig. 627, p. 319) shows the relations of this 

 water-conducting tissue to the surface, and an examination of the vena- 

 tion of various leaves (of which only the larger veins are visible to the 



