229 
the Sporophylls of the Cycadaceae. 
passes obliquely away to the far side of the sporangium, 
remains undivided. As seen in transverse section, a bundle 
about to enter the sporangium has a curved contour, with 
very well-developed centrifugal and often a large amount 
also of centripetal xylem ; the occurrence of this latter is 
perhaps correlated with the evident tendency of these bundles 
to revert to a concentric structure. 
In many of the bundles in the most distant portions of 
the lamina, transfusion-tissue is very markedly developed, 
resulting from the extension, even on to the dorsal side 
of the phloem, of the centripetal xylem (Fig. 23). As in 
nearly all other cases, the tracheides of the centrifugal are 
always much smaller than those of the centripetal xylem. 
Zamia furfuracea, Ait. 
Female SporophylL In the stalk are four bundles with 
the usual structure ; no centripetal xylem occurs here ; the 
two lateral bundles are rather better developed than the 
others and have larger centrifugal tracheides. A little higher 
up in the sporophyll one of the middle bundles gives off 
a very small branch which gradually, in passing upwards 
and towards the ventral side, turns on its axis, assuming 
directly afterwards a perfectly concentric structure, which 
again, higher up, opens out and becomes collateral ; there 
may be more than one bundle on the ventral side of the 
normal row ; these bundles pass up into the lamina without 
again assuming a normal orientation. In this latter region 
of the sporophyll transfusion-tissue is well developed in many 
of the bundles. 
Two bundles enter each megasporangium ; one of these, 
the largest, being the lateral, unbranched bundle of the stalk 
on the same side which passes up round the axil of insertion 
of the sporangium ; the other, which is very much smaller, 
as a descending branch from a bundle which has passed 
a considerable distance up into the lamina ; there is thus 
