209 
the Sporophylls of the Cycadaceae . 
the single large concentric strand entering the central 
chalazal portion of the sporangium, and which breaks up 
into a group of bundles radiating from the common centre to 
the different parts of the organ, it will hardly entirely account 
for the extremely small concentric bundles occurring in no 
very definite position in the group, and which must necessarily 
take a subsidiary part in supplying the sporangium. I am 
inclined, on the other hand, to regard these concentric 
structures and the constancy with which they occur in the 
region concerned, as relics of the original primitive structure 
appearing in what must be considered as the most primitive 
tissue of the sporophyll. 
It is the function of the individual bundles of the sporophyll, 
both on the male and female side, which readily explains their 
various degrees of development and varying types of structure. 
The bundles of the male sporophyll, at the level of the 
insertion of the sporangia, are small and insignificant in 
appearance because each one is told off to supply one of the 
numerous small sori scattered over the surface of the sporo- 
phyll, the microsporangia composing each having but a very 
temporary existence, insomuch that the function of the bundle 
supplying them ceases with the dispersion of the spores. 
Even in the lowest region of the stalk, before much branching 
of the bundles has occurred, and where they are therefore 
somewhat larger and fewer in number, the latter have quite 
a small development of centrifugal xylem as compared with 
that of the bundles supplying the megasporangia, this being 
clearly correlated with the respective functions of these bundles. 
But why in some genera the bundles in the basal region of 
the stalk of either male or female sporophyll should possess 
centripetal xylem, while in the case of other genera this 
tissue should be quite absent, and why this variation should 
exist both between the bundles of sporophylls of opposite 
sexes and between the bundles of one and the same sporo- 
phyll, is no more obvious than the reason why the same 
variation in structure should prevail in the bundles of the 
peduncle, not only of different genera, but also of different 
