16 BOTANICAL GAZETTE [JANUARY 
in fig. 34. The foliar traces are more numerous at this level, and 
are beginning to draw in toward the fibrovascular cylinder of the 
main axis. It will be seen that the bundles of the axis are amphi- 
vasal in the upper middle region. On the left is one of the bundles 
of the branch pursuing a tangential course to become fused with 
the face of the more lateral bundles of the cylinder of the main 
axis. The bundles of the main stem become amphivasal for nearly 
two-thirds of the perimeter of the cylinder before the union: of the 
branch with the parent axis is completed. One of the amphivasal 
strands from the median upper region of fusion is shown in fig. 36. 
It is clear that the organization is quite similar to that of the 
Monocotyledons, the only contrast being in the presence of 
secondary growth. This, however, is not a matter of great impor- 
tance from the evolutionary standpoint, since often in the Mono- 
cotyledons secondary activities can be recognized in the nodal 
region of the stem, as has been pointed out by CHRYSLER (1) and 
others. It is of interest to observe that in this genus the fusions 
which result in the formation of amphivasal bundles take place 
on the outside of the fibrovascular ring and not internally as in 
the buttercup. This situation seems to be rather a common one 
for the Umbelliferae as a whole. As the nodal region is passed 
the amphivasal bundles open up toward the outside of the stem 
and constitute dense, flat, fibrovascular segments of collateral 
organization. Similar conditions in regard to the resolution of the 
amphivasal strands are found in the buttercup. 
Fig. 37 illustrates the organization of the stem in the nodal 
region of Rumex sp. The foliar traces are numerous, and to a 
_ large extent have passed into the cylinder. The periphery of the 
medullary region is occupied by a number of fibrovascular bundles 
of amphivasal organization. ‘These are the result of the fusions of 
strands of the secondary and main axes by their phloems. The 
amphivasal strands in lower regions of the internode undergo fusions 
with the bundles of the cylinder, and finally completely disappear 
before the next node is reached. Fig. 38 shows a part of fig. 37 
more highly magnified.. The amphivasal strands can be seen on 
the medullary side of the collateral bundles which constitute the 
main cylinder. 
