194 Sargant and Arber ,— The Comparative Morphology of 
elements are commonly external to the rest, it is not surprising that the 
mesocotylar stele of Zea has been described as root-like. 1 This is, however, 
a mistake. The plumular traces, as well as those connected with scutellum 
and coleoptile, are certainly of the usual stem-type ; that is, their xylem is 
centrifugal, and internal to the phloem. 
We have now described the anatomy of the mesocotylar stele near its 
base, and its connexion with the scutellum trace. Following it upwards, 
we find some changes in a transverse section taken just below the first node. 
Much of the root xylem has died out, and what is left is thin-walled 
and unlignified. The two phloem bundles on either side of px x (ph lf ph^ 
pH and pH ^ sometimes divide into three or four groups. In one seedling 
two small groups, one on either side of px v appear to represent a pair of 
minor plumular bundles whose insertion on ph x and pH x respectively has been 
delayed for some distance below the node. The two or three groups beyond 
them represent ph x and ph 2 on one side, and ph\ and plf on the other. 
Here, as in Sorghum, the first node is most easily described from 
above downwards. The plumular traces are very numerous, even in these 
young seedlings, but mostly small and unlignified. The midrib M of the 
first leaf can be traced with certainty through the complications of the 
node into the mesocotylar stele. The other traces anastomose with each 
other, and most of them finally settle down into the single semicircle shown 
in Text-fig. 21. A few insert themselves on the coleoptile traces at or near 
the node. 
The coleoptile traces themselves are clearly double, with two well- 
marked phloem groups side by side, and groups of xylem internal to both. 
There is a common group of protoxylem, and lignification of the metaxylem 
seems to start on either side of it, suggesting that in older seedlings the 
metaxylem will be in two groups like the phloem. The traces do not 
divide until they have entered the stele. They approach each other from 
opposite directions in the same straight line ; so that the two larger xylem 
branches, maintaining their original direction, meet to form a massive 
xylem bridge, which divides the circular stele into two unequal segments. 
The two smaller xylem branches bend outwards, and meet almost at once 
to form the peripheral protoxylem group px v 
We have already described the mesocotyl just below the node in one 
seedling. In this instance the two phloem groups of each trace, together 
with the plumular phloem inserted on them, give rise to three or four 
groups in the stele just below the node. Lower down these unite to form 
the two groups ph v ph 2 , on one side oi px v and pH ^ pti 2 , on the other. We 
do not doubt that the two groups in each pair represent the two phloem 
groups of a single coleoptile trace, but they do not seem to maintain their 
1 Schellenberg and Kirchner in Kirchner, O. von, Loew, E,, and Schroter, C. (’o8-’i2), 
p. 231. 
