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 F IG- 638. Ending of a xylcm strand among the cells of the 
that Only a few mesophyll in a leaf of lilac (Syringa vulgaris) : t, tracheid ; i, 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- 
FIG. 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 
