the Sporophylls of the Cycadaceae. 207 
entirely supplanting the other, and vice versa. The very 
frequent presence here of the bundles with an endarch 
structure probably indicates the far-reaching influence of the 
special physiological function of the sporophyll, which causes, 
even in the region where it can no longer have any meaning, 
the suppression of the centripetal in favour of the centrifugal 
xylem. In the extreme portions the bundles are often 
reduced to a few irregular large tracheides. Transfusion- 
tissue is of very frequent occurrence in connexion with the 
bundles, and is sometimes of considerable development. 
In the female sporophyll there are usually about four, some- 
times a larger number, or only two bundles to be seen in the 
stalk. Two bundles arise independently, as a rule, from two 
distinct members of the central cylinder of the axis ; these, 
where a larger number supplies the sporophyll, divide up in 
the cortex before entering the latter. 
The structure and behaviour of the bundles in the female 
sporophyll are essentially the same as has been described for 
those in the male organ ; but the difference in sex of the 
sporangia, necessarily involving a difference in their function, 
a great reduction in their number, a considerable increase in 
their individual size, and an altered position on the sporophyll, 
goes hand in hand with a certain difference in the develop- 
ment of the bundles. The bundles which are told off to 
supply the sporangia are, in most cases, two in number, one 
at either side of the much elongated stalk ; each of these 
branches in the base of the expanded portion, sending off one 
or two bundles for the sporangium, which in nearly all genera 
is situated at the margin of the sporophyll in the sinus formed 
by the reflexed lateral portion of this part of the sporophyll, 
or on the tip of the reflexed portion, so that its apex is 
directed towards the axis of the cone. There is considerable 
variation in the number of the bundles which enter the 
sporangium and in the amount of branching which takes 
place after the one or two strands have been given off from 
the bundle proceeding from the stalk. The two lateral 
bundles in the stalk which supply the sporangia are always 
