636 Sargant.—A New Type of Transition from 
figured here, taken about the level marked by a dotted line 
through A 3 in Fig. 1. The outline of the section is still 
oval, but a slight groove marks the inner surface of the 
cotyledon. 
The preparations drawn in the four following figures (3-6) 
are from a microtome series through the region marked by 
a bracket in the outline of A 3 (Fig. 1). The first (Fig. 3) 
passes through the embryonic stem-bud enclosed in the 
sheath-like base of the cotyledon. Besides the two massive 
bundles of the cotyledon, the section shows three procambial 
strands in the first leaf. The section drawn in Fig. 4 is 
•34 m.m. below this. The plumular traces, still embryonic 
in character, are entering the stele formed by the cotyle¬ 
donary traces. This marks the first node of the young axis, 
and the upper limit of the hypocotyl proper. The two lateral 
plumular traces (B and C) are in the act of joining the stele. 
The plumular midrib A has divided, and its branches follow 
B and C respectively. The transition to a root-structure has 
already begun in the cotyledonary stele by the division of each 
large phloem-mass. Each cotyledonary trace has now a pair 
of phloem-groups, and a single wedge-shaped mass of xylem 
with well-marked internal protoxylem (Fig. 4). 
The fusion of the plumular traces with those of the coty¬ 
ledon is complete at the level of Fig. 5, which is drawn from 
a section cut -3 m.m. lower than that drawn in Fig. 4. In 
this section (Fig. 5) the protoxylem-group of each cotyle¬ 
donary trace has divided into three parts, each of which 
is on the way to become external. The medium protoxylem 
group of each trace (px^, and pxi) will ultimately divide the 
two branches of each phloem-group from each other. That 
is, px v when completely external, will divide Pk 1 from Ph 2 , 
and pXj± will divide Ph 1 / from Ph 2 '. The two lateral proto- 
xylem-groups of each trace will occupy the space inter¬ 
mediate between the two traces ; px% and pxi dividing Ph x 
from Phi, and px z with pxi dividing Ph. ± from Phi. 
This process is almost complete in the section drawn in 
Fig. 6, which is -35 m.m. below that drawn in Fig. 5. All 
