217 
the Sporophylls of the Cycadaceae. 
and exceedingly small. They are here seen to possess one 
or two centrifugal and one or two centripetal tracheides ; 
there is a very small quantity of phloem ; no definite cambium 
can be distinguished, so that it is possible that the centrifugal 
tracheides are primary. The bundles are arranged in an arc. 
Sclerotic cells are scattered about in the ground-tissue. 
The uppermost scales are more leaf-like and much broader 
than the lower scales, and represent sterile sporophylls, re- 
sembling in shape the fertile organs. One of these, whose 
structure was examined, has an extremely long foliar base, 
running ridge-like, a considerable distance down the peduncle. 
About half way up this foliar base a minute concentric bundle 
becomes differentiated from the ground-tissue, arising quite 
independently of any other strand (Fig. io). Higher up it 
gradually increases in size, and in the upper free part of the 
organ is observed to give rise to an imperfect branching 
system forming the nervation of one side of the sporophyll. 
About three or four branches occur, all very imperfect, 
interrupted for considerable spaces in different parts of their 
course, and dying out before reaching the margin of the 
sporophyll ; they appear to have a very reduced structure, 
and their tracheides are much twisted and contorted. From 
their evident progress towards extinction and the concentric 
structure of the bundle from which they spring, they may be 
said to represent part of the original primitive bundle-system 
of the sporophyll which has long since ceased its connexion 
with that of the peduncle. A portion of the system, however, 
has still retained this connexion, and after a large part of the 
sporophyll became fused with the peduncular tissues, the 
bundle constituting the base of this system assumed a more 
direct course into the axis, passing in in the upper part of 
the foliar base, instead of, as in the case of the small con- 
centric bundle, running down in the latter towards its 
lower extremity. This bundle, which enters the barren 
sporophyll from the peduncle, possesses, whilst still in the 
latter, two distinct and well-marked groups of centripetal 
xylem. The subsequent course and branching of this bundle 
Q 2 
