406 Scott. — On Peduncle of Cycadaceae. 
peduncle, is the only point of any importance in which it 
differs from the corresponding tissue in the leaf. This, how- 
ever, proves nothing against the homology between the two. 
In the peduncle of Cycads the centripetal part of the wood is 
a vestigial structure, and it is well known that vestigial organs, 
when recognizable in the adult, are usually late in completing 
their development. 
Even in the foliar organs, the relative periods of develop- 
ment of the two parts of the wood is extremely variable, as 
is indicated by their variable relations to the protoxylem- 
elements. In the sporophylls of many Cycads the centripetal 
portion of the wood is excessively reduced and may even be 
altogether absent. In such cases the spiral elements are 
always in immediate connexion with the centrifugal wood 
(see Figs. 12 and 13). In the carpel of Ceratozamia the centri- 
petal wood is developed late compared with the centrifugal 
portion, and no doubt this is often the case, where the former 
tissue is reduced. 
The peduncle and axis of the female cone of Stangeria, 
like those of the male, show centripetal xylem in connexion 
with some of the bundles. In the specimens available, how- 
ever, it was much less developed than in the male cone. 
Here also the elements in question are shown, by longitudinal 
sections, to be scalariform tracheides. 
As a rule, the centripetal wood, whether in the male or 
female peduncle, is limited to the principal bundles of the 
stele. No clear case of the presence of this tissue in a leaf- 
trace passing out to a functional sporophyll has been observed, 
nor is this surprising, considering the excessively slight 
development of centripetal xylem in the bundles of the 
sporophylls themselves. In some cases certain small bundles, 
passing through the cortex, were found to have a few centri- 
petal xylem-elements ; but such bundles appear to be either 
purely cauline, or to be destined for the bracts or sterile 
sporophylls which occur at the base of the actual cone. In 
these the centripetal xylem is somewhat better developed 
than in the fertile sporophylls. 
