2io Worsdell . — The Vascular Structure of 
species, as has recently been clearly observed 1 . The greater 
or less development of the centrifugal portion of the bundle 
does not appear to be the sole or even the principal con- 
ditioning factor in determining the amount of centripetal 
xylem present, for where the latter is fairly well represented, 
the centrifugal portion may be better developed than in those 
cases where it is absent. There is evidently in these organs, 
as in the peduncle, the axis of the cone, and the foliage-leaf, 
a tendency, in spite of other prevailing influences, for the 
primitive mesarch characters to appear in the bundles, this 
tendency being stronger in some genera than in others, 
notably in those in which the sporophylls are of large size, 
this latter being doubtless indicative of their more primitive 
character as compared with the smaller and more highly 
modified sporophylls of other genera. 
In the cones of both sexes of all genera there are always, 
at the base of the cone, a number of sterile sporophylls, which 
may either have the form of the fertile organs and be crowded 
together like these, or may be elongated structures more like 
bracts in shape and position ; frequently a gradual transition 
occurs between these latter and the normal fertile sporophylls. 
It is interesting to note that the vascular structure of these 
barren sporophylls, while partaking in a general way of that 
of the fertile organs, exhibits a more primitive character, owing 
chiefly to the fact of the absence of the sporangiferous 
function in these organs, whereby these primitive structures, 
which consist of the more frequent presence of concentric 
structures and the occasional abortion of parts of the vascular 
system, have not been so much interfered with and altered as 
in the case of the fertile sporophylls. The small bundles in 
the cortex of the upper portion of the peduncle of both sexes, 
which are usually observed in pairs, and which supply the 
sterile sporophylls, possess very often a small quantity of 
centripetal xylem 2 , which is frequently developed as trans- 
fusion-tissue both in a ventral and lateral position. 
Scott, loc. cit. 
2 Cf. Scott, loc. cit., p. 406. 
