WorsdelL — The Structure and Origin of the Cycadaceae. 149 
There thus appears a mass of clear and conspicuous evidence in favour 
of the derivation of both the primary and the secondary end arch rings or 
cylinders of Cycadean stem-organs, from the poly- or solenostelic structure 
of the same organs in the Medulloseae. The hypothesis of the appearance 
on the scene of a meaningless cambium in order to account for the inverted 
ventral strands, I find myself quite unable to accept. 
2. Origin of Foliar Structures. 
The Fern-like character of the foliage of the Pteridosperms we found 
to be still represented in that of certain of our modern Cycads. We 
should therefore expect to find in the anatomy of the foliar organs of 
Cycads further indications of their Pteridospermic ancestry. 
Fig. 14. 
Fig. 13. Medullosa stellata : transverse section of leaf-trace bundle just after leaving central 
cylinder, showing the three component parts into which it eventually splits (diagrammatic and 
partially restored) (after Weber and Sterzel). Fig. 14. Stangeria paradoxa\ transverse section 
of three sets of leaf-traces, two of which are broken up into their constituent strands, the other being 
entire (diagrammatic). 
Firstly, I may refer to the structure of the vascular bundles. In 
Medullosa the leaf-trace bundles on leaving the central cylinder of the 
stem are perfectly concentric (Fig. 13), but shortly each breaks up into 
a number of collateral strands. In Lyginodendron and Heterangium 
the bundle only assumes the concentric structure after entering the leaf, 
where refusion of the two, which were the result of division of the leaf-trace 
in the pericycle, takes place. But in certain stems of Lyginodendron some 
of the leaf-trace bundles were perfectly concentric in structure. 
Now I observed in the peduncle of the female cone of Stangeria that 
some of the sporophyll-traces immediately on leaving the central cylinder 
appeared in the form of three separate small bundles grouped around 
a common centre, so that such a group may be said to represent, as 
it were, a fragmented concentric bundle. Further out in the cortex 
these bundles became completely separated from each other. In the 
