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 FIG. 638. Ending of a xylem strand among the cells of the 

 that only a few mesophyll in a leaf of lilac (Syringa vulgar is) : t, tracheid; ^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 Ficus, 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 



