192 Sargant and Arber.—-The Comparative Morphology of 
axis—the ‘ wedging ’ roots as we have called them ( 1 . c., PL V, Figs. 6-9, r). 
The median segment is the most slender of the three. It goes straight to 
the axial stele, and at once turns upwards within it. The two phloem 
strands accompany the scutellum xylem, one on either side of it. Each 
gives off a considerable portion to the stele of the nearer wedging root on its 
way to the axial stele. Thus the scutellum xylem enters the latter with 
a phloem branch on either hand, and they turn upwards side by side 
with it. 
These three strands, one of xylem and two of phloem, can be followed 
from their entrance into the mesocotylar stele upwards to the first node in 
m 
Text-fig. 21. Zea Mays , L. Diagram of mesocotyl as seen in transverse section. 
two seedlings. Both of them are young, with the stem-bud still completely 
enclosed in the coleoptile. The cauline roots which will be produced later 
from this node are not present even as rudiments, though a band of meri- 
stem partly enclosing the stele suggests the formation of new members 
there. So far, indeed, the youth of the seedling is an advantage, since 
it allows the primary structure of the node to be followed without the com¬ 
plications introduced by root-insertions. But on the other hand the 
mesocotylar stele is very imperfectly differentiated at this age. After very 
careful inspection of these two complete series, and comparison with 
several partial ones from seedlings of the same age or older, we found 
certain landmarks within the stele which enabled us to interpret its structure 
