( Intrcixylary) Phloem in the Stems of Dicotyledons. I. 585 
a large amount of xylem, most of which is parenchymatous, but with 
a small group of fibres developed towards the outer side. 
On the other hand, the xylem on the outer side of the internal phloem 
of the outer series of bundles is, in almost every bundle, much more greatly 
developed both as regards parenchymatous and woody elements, sometimes 
equalling that of the bundle itself; both the external and internal phloem 
Fig. 6. Acanthosicyos horridus. Trans¬ 
verse section of peduncle, showing two rings 
or series of bundles, each with its internal- 
phloem bundles ( ipK ). rb, vascular bundle 
of the normal ring; sr, sclerotic zone, 
x 11. 
Fig. 7. Acanthosicyos horridus. Trans¬ 
verse section of a single bundle of the ring 
with its internal-phloem bundle (iph'); the 
essential amphivasal structure of the latter 
is shown by the cambium situated on its 
medullary side, x 30. 
are very arc-shaped with the concavities, filled with the xylem, opposed to 
each other ; the internal phloem is also much radially extended. The whole 
resembles a large concentric (amphiphloic) bundle incompletely built up 
owing to the presence of two wide rays, one on either side, representing the 
ground-tissue areas separating the two large vascular bundles. 
Stipule. 
A cylindric organ resembling a small twig in its structure. 
The outer series of bundles, situated in the bays between the sclerotic 
intrusions, is much better developed than the inner series. The latter 
are more or less rudimentary, with an almost complete absence of internal 
Q q 2 
