220 WorsdelL — The Vascular Structure of 
extremely minute, with centrifugal xylem only, the tracheides 
of which are well defined and thick-walled. The bundles are 
very irregular in position and orientated in different directions. 
In the sterile portion the centrifugal xylem is much reduced 
and quite insignificant. The centripetal xylem is fairly well 
developed and its tracheides much scattered and wandering. 
In some of the bundles the phloem is scarcely developed, and 
the parts of the xylem cannot be properly orientated. 
Female Sporophyll. Two bundles leave the central cylinder 
of the axis of the female cone ; in the outer part of the cortex 
each of these divides into two, so that four bundles are 
produced. In those cases where other bundles, besides these 
four, occur, in the stalk of the sporophyll, these are cut off by 
the two original bundles just before entering the latter, and 
passing off towards the ventral side of the sporophyll, they, in 
the majority of cases, twist on their axes, assuming thereby 
a more or less abnormal orientation (Fig. n). The number, 
orientation, and structure of these ventral bundles in the stalk 
varies greatly ; the following are the principal cases met 
with : — 
1. One large bundle with inverted orientation. 
2. Three bundles, two with inverted orientation, and the 
median one concentric (Figs, n and 12). 
3. Two bundles, closely contiguous, lying sideways with 
their xylems facing each other. 
4. Two bundles, one of which lies sideways, the other 
obliquely. 
5. One bundle, lying close on the ventral side of one of the 
normal bundles, and with normal orientation, but placed 
rather obliquely. 
6. One bundle, lying sideways. 
7. One bundle, with normal orientation. 
All the ventral bundles pass up into the lamina, without 
taking any part in supplying the sporangia ; those which in 
the stalk were inversely orientated, in the lamina twist on 
their axes once more to assume approximately the normal 
orientation. Here the same change as regards the relative 
