586 
MR. F. O. BOWER ON THE COMPARATIVE MORPHOLOGY OF THE 
muricata ,’ p. 197), it is only comparatively late stages of development which have 
hitherto been observed. Hence, though the conclusions drawn are probably correct, 
they cannot be regarded as having been conclusively proved. (An exception may be 
made in the case of Ceratozamia observed by Warming.) 
In the case of young plants, such as the seedlings of C. Seemanni, there are practical 
difficulties in the way of a certain decision : thus the number of pinnae on one leaf is 
comparatively small, while here, as in other cases among the Cycadacece, they arise 
almost simultaneously, and first appear as very slight undulations on the wings of the 
phyllopodium. Still, by comparison of a considerable number of cases, the conclusion 
has been arrived at that there are, in the case of C. Seemanni, distinct signs of a 
development of the pinnae in acropetal succession: the pinnae close to the apex, even 
in the youngest cases observed, are smaller than those lower down, while, in some 
instances at least, a similar diminution in size was observable in passing downwards 
towards the base of the leaf (Plates 38, 39, figs. 27, 28). These observations on leaves 
of young plants cannot be regarded as entirely satisfactory, but they acquire greater 
value when coupled with observations on an old plant of C. Jenkinsiana, to be detailed 
below, and with those of Warming ( l.c .) (cf. infra, p. 589). 
The question remains whether there is any regular alternation in the appear¬ 
ance of the pinnae on opposite sides of the phyllopodium. Some examples show 
that there is such an alternation, and this may be seen especially in the pinnae 
nearest to the apex of the leaf. It was the prevalence of such alternation at the apex 
of the leaf of certain Cycads ( e.g ., C. revoluta), which no doubt gave rise to the idea 
that the leaves develop sympodially. In other examples of C. Seemanni, no such 
alternation is to be found, and comparing the leaves, both young and mature, in a 
considerable number of cases, it is clearly seen that the arrangement of the pinnae is 
neither constantly in opposite pairs nor regularly alternate on opposite sides of the 
leaf. 
Finally, the position of the pinme at the apex of the mature leaf of C. Seemanni 
appears to illustrate the transition from the lateral to the terminal position. But, 
judging from young stages of development, I think it improbable that the apex of the 
phyllopodium, in this species at least, ever develops as a true winged structure; but 
rather that the apparently terminal pinna sometimes to be found is originally lateral, 
and gradually assumes the apparently terminal position as development proceeds. An 
accurately terminal pinna has never been observed in an early state of development, 
though one pinna may sometimes be nearer the apex than the rest, as in Plate 3S, 
fig. 27. A comparison of a number of mature leaves of this species leads to the 
conclusions (1) that one apparently terminal or obliquely terminal pinna is about as 
frequent as two more or less exactly equal ones, and (2) that there is no apparent 
tendency for the older leaves to be more regular in this respect than the younger ones. 
Up to the point of formation of the pinnae, the development of all the leaves is 
alike, whether they appear when mature as foliage-leaves, or as the well-known scale- 
