Phloem in the Stems of Dicotyledons . II. 425 
rise by branching to a fresh system in that region, all of which are vascular 
bundles and are closely contiguous to the xylem of the ring-bundles. 
The above-described structure obtains in the lower region of the stem. 
At a node in a higher region of the stem where a branch is given off, 
two or three of the peripheral medullary bundles, occurring on the side on 
which the branch and the leaf-bundles are inserted, increase much in size 
from below upwards and become incompletely amphivasal in structure ; they 
eventually anastomose with the bundles of the ring, and then pass outwards 
through the gap to form the adaxial portion of the vascular cylinder of the 
branch, becoming perfectly amphivasal before doing so. 
The medullary strands of the stem pass up into the peduncle , in the 
lower part of which they consist of phloem only. As the lacuna makes its 
appearance the central strands die out in situ> so that in the higher part of 
the organ the strands, which have here nearly all acquired a little xylem on 
their outer side, are peripheral, one occurring opposite each bundle of the 
ring and forming with it the vascular supply of a floret. 
Stem z. 
This was a thicker-stemmed individual than the last. In the swollen 
subterranean portion of the stem, at the level of insertion of the lowest leaves 
and where, as seen in transverse section, the leaf-traces are passing out, two 
or three vascular bundles arise de novo at the periphery of the pith. Here 
we see a difference from what obtained in the individual last described, 
where the first-appearing medullary strands arose from the vascular ring. 
Almost at the same time as these bundles arise de novo they form 
connexions with the vascular ring : this case may be thus regarded as 
a transitional one between those in which the bundles arise de novo and 
maintain for some distance an independent course and those in which the 
bundles arise from the vascular ring. A short distance below where these 
bundles arise the pith is seen to be full of short tracheides scattered 
promiscuously through the tissue. 
The medullary bundles at once divide up and anastomose together and 
give off branches into the centre of the pith. The large peripheral ones 
appear to be directly connected with the leaf-traces, but are not direct 
continuations of these last, which is a very different thing. Rather smaller 
bundles occur here and there in the embouchement of the rays. 
At a higher level, the bundles of the two medullary systems, viz. the large 
anastomosing peripheral, and the.smaller, central, branching bundles, become 
entirely devoid of lignified xylem. At a still higher level, viz. at about the 
top of the swollen underground portion of the stem, the central strands die out 
in situ for the most part, but a few of them unite with the peripheral ones. 
From a study of the medullary system of the stem in these two 
