228 
Journal of Agricultural Research 
Vol. XIV, No. 6 
node. This behavior of the bundles continues uniformly at succeed¬ 
ing nodes. 
To summarize: 
(1) The median trace ascends without fusion or forking through three 
intemodes, and then passes into the people without branching. 
(2) The lateral traces are given off at the node from two of the three 
large stem groups. 
(3) Each large stem bundle ascends without branching in turn for 
two intemodes and for one intemode. 
(4) Where a large stem bundle ascends for but one intemode without 
branching, it divides three times, giving rise upon the first division to 
a new stem bundle, upon the second division to a new median trace, 
and upon the third division to lateral traces of the petiole. Upon the 
division in the node, half of the tissue given off to unite with that from 
the left (in a right spiral) adjacent group, forming a new large bundle 
directly above the insertion of the leaf. Where the bundle ascends 
for two intemodes without branching, it gives off vascular tissue only 
for lateral traces of the petiole. 
(5) Each leaf derives its supply from two large bundles and the 
smaller one lying between these. The method of derivation is uniform 
for all leaves, the bundles taking part being each time a different pair 
from those supplying the leaf below. In a right spiral the right member 
of the set supplying a leaf supplies also the leaf above, becoming there 
the left member of the set. The median trace of a given leaf is formed 
just below the third node below the leaf it supplies. 
The vascular tissue shows bicollateral arrangement of its elements, a 
condition most clearly seen in the larger bundles of the stem. An 
examination of Plate 29, A, shows at first glance a wedge-shaped mass 
of rather large, dark-staining cells, the xylem. At more or less equal 
distances to the outside and the inside of the xylem are small groups of 
thin-walled cells which make up the phloem. The external phloem is 
separated from the xylem by a layer of uniform, rectangular cells, the 
cambium. The internal phloem is also separated from the xylem, but 
in this case by thin-walled, irregular cells (PI. 29, C). These cells are 
much smaller than those of the pith and form what may be called the 
perimedullary zone of the vascular cylinder (stele). The external 
phloem groups are separated from one another and from the endodermis 
by parenchymatous cells of irregular size, which together constitute the 
pericyclic region of the stele (Pi. 29, A, B). The internal phloem abuts 
directly on the pith, and many of its groups are completely surrounded 
by pith cells. The phloem in both regions is made up of cell groups 
which in the outer zone are small and form a more or less continuous 
band and which in the inner region are variable in size and more scat¬ 
tered (PL 29, C). . x 
