234 Worsdell . — The Vascular Structure of 
the normal row, several small normally-orientated bundles 
whose origin, owing to the cone being in a state of decay and 
the tissue therefore connecting the sporophylls with the axis 
being partially destroyed, could not be ascertained (Fig. 27). 
In the case of a small bundle 'with inverted orientation, lying 
on the ventral side of one of the large lateral bundles, this 
was observed to be cut off from this latter, whose phloem 
gradually extended round the xylem, so as to render the 
bundle partially concentric in structure, when part of it 
became severed towards the ventral side, which part, twisting 
on its axis, formed the small inverted bundle. 
In the lamina, the bundles have usually an equal quantity 
of centrifugal xylem, but in some the latter is absent. 
In the young female sporophyll the developing bundles of 
the lamina appear to form centrifugal and centripetal xylem 
at the same time ; in some bundles both kinds are seen 
together (Fig. 28), in others centripetal alone ; in others, again, 
centrifugal alone ; in some there is an intermediate stage 
where the tracheides lie at the side of the protoxylem. This 
variation in the respective development of the centrifugal and 
centripetal xylem coincides with what is found in the mature 
sporophyll. 
In the barren sporophyll of this genus the bundles are all of 
uniform development, and none are so markedly developed as 
those supplying the sporangia in the fertile sporophyll. 
Summary. 
The result of my investigations into the structure of the 
sporophyll for each genus may be thus summarized: — 
Cycas, $ : in lower part of stalk (though probably not at 
extreme base) centripetal xylem of bundles is equal to, 
or greater in amount than, centrifugal xylem. 
? : borne directly on vegetative axis ; larger and 
more leaf-like than in any other genus ; bundles of 
large size, with large development of centrifugal and 
