LEAF IN THE VASCULAR CRYPTOGAMS AND GYMNOSPERMS. 
589 
investigating them developmen tally or anatomically, the scale-leaves are to be 
regarded simply as altered foliage leaves, which might have developed as such, but 
are arrested at an early stage ; their basal portion is proportionally widened, and 
their apical part aborted (compare Onoclea, Osmunda, and Todea barbara). 
Cycas Jenkinsiana, Griff. 
The above observations on seedlings of Cycas Seemanni not having been quite 
conclusive on the point of the order in which the pinnae appear, it was desirable to 
control them by observations on some older plant, the lea.ves of which produce a large 
number of pinnae. Cycas Jenkinsiana was selected for this purpose ; the individual 
plant bore on one leaf about forty pinnae on each side, those on opposite sides being 
arranged in more or less regular pairs. In addition to these there were about ten 
pairs of spines on the lower part of the leaf, corresponding in position to the pinnae, 
and, as will be shown below, produced in the same manner as the pinnae with which 
they are homologous. The young leaf of this species is similar in general confor¬ 
mation to that in C. Seemanni ; it consists of a central columnar portion, on which 
are formed two lateral, longitudinal ridges. These are most strongly developed at 
the base of the leaf, forming a more prominent sheath than in C. Seemanni; they 
may, however, be clearly traced as continuous to the apex of the leaf, which is 
thus in its early state a simple winged phyllopodium. 
The numerous pinnae make their appearance almost simultaneously throughout the 
entire length of the lateral wings, as gentle undulations, which gradually assume 
the form of rounded papillae. There is a slight but unmistakable indication of a 
priority of appearance of those pinnae which are formed about the middle of the 
leaf, while those nearer the apex and the base appear rather later (Plate 39, fig. 30). 
This observation thus corroborates that of Warming ( l.c Taf. 3, fig. 20), though the 
difference seems to be less marked here than in Warming’s specimen of Cycas 
circinalis. In the development of the normal pinnae there is no difference from 
C. Seemanni requiring further remark ; but as may readily be seen at the lower 
part of the mature leaf, there is a gradual transition downwards from the normal 
pinnae to reduced spinous structures, which occupy a position similar to the pinnae, 
and are doubtless due to arrested development of homologous structures. This 
view is thoroughly borne out by observations of their development. It may be 
seen in leaves in which extension has not begun, that the formation of pinnae 
is continued along the wings in a basipetal direction almost down to the sheath. 
It is just above the sheath that the petiolar extension begins, and it is most 
marked over the lower part of that region on which pinnae have already appeared. 
These lower pinnae are thus separated a considerable distance one from another 
(Plate 39, fig. 31), at the same time they remain in a comparatively rudimentary 
state, and do not keep pace with the increase in size of the pinnae above the region 
