2 I i 
the Sporophylls of the Cycadaceae. 
I will now proceed to describe the structure of the vascular 
bundle-system of the sporophylls of the various genera of 
the order. 
Cycas revoluta, Thunb. 
Male Sporophyll. The few sporophylls available for 
investigation were supplied from a male cone preserved in 
spirit in Museum No. I in the Royal Gardens. On this 
account the course of the bundles from the central cylinder of 
the axis of the cone to their entry into the sporophyll was 
not observed ; but this has been adequately followed in 
C. siamensis Miq. and C. circinalis L. by Thibout \ who finds 
that a single bundle enters the cylinder from the sporophyll. 
The sporophyll does not assume such a perpendicular position 
with regard to the axis of the cone as in most genera, but is 
more or less curved. It is also larger, not being quite so 
reduced in size as in other cases. There are a number of 
bundles in a row whose size is in correspondence with that 
of the sporophyll. They possess sharply defined centrifugal 
xylem in fair quantity. Most of them have an almost equal 
quantity of centripetal xylem ; but the latter, in one or two 
cases, far exceeds the centrifugal, consisting of a great number 
of elements extending some distance from the protoxylem. 
The tracheides of the centripetal are often far larger than 
those of the centrifugal xylem. But in every case the 
centripetal is less brightly and sharply stained than the 
centrifugal portion, this fact indicating that the latter is more 
strongly lignified and thus chiefly functional in conduction. 
The chief feature of the structure of these male sporophylls 
of Cycas is the appearance, in the bundles of the lower portion 
of the stalk, of centripetal xylem. In no other genus is this 
tissue so well-developed in this region of the sporophyll, and 
it affords an instance of the way in which the centripetal 
tracheides may form the chief part of the xylem quite low 
down in the stalk. In the sterile portion the centrifugal 
1 Recherches snr l’Appareil Male des Gymnospermes, 1896. 
