LEAF IN THE VASCULAR CRYPTOGAMS AND GYMNOSPERMS. 
591 
had already been formed in considerable numbers, it was clear that the development 
proceeded in a basipetal direction. This could be proved as follows, on the assump¬ 
tion that leaves formed subsequently to those already developed would form approxi¬ 
mately as many pinnae as they. The foliage-leaf of this plant of Dioon formed about 
50 pinnae on each side. In one young leaf, which showed no sign of apical growth, 
there were about 25 pinnae on each side, while those nearer the base were successively 
smaller than those above, till their identity was gradually lost in the smooth ridge ; 
a considerable space, however, intervened between the lowest traces of' the undulation 
and the sheathing wings. These facts being so, and the next older leaf having a 
larger number of pinnae, while the next younger one had fewer, the conclusion may 
be safely drawn that there is a formation of pinnce in basipetal order of succession. 
But this does not exclude the possibility of a simultaneous development in an acro- 
petal succession, at least among the earliest formed pinnae, and the observation of 
younger leaves, in which the formation of pinnae is just beginning, gives good evidence 
that there is also an acropetal succession, which is, however, soon arrested. Thus on 
the youngest leaf of the plant in question, which bore any traces of pinnae, it was 
distinctly seen that those at the extreme apex of the leaf were smaller than those 
slightly lower, while those lower still were again smaller (Plate 39, fig. 32). This 
appearance not being supported by observations of more than a single specimen, is 
capable of two interpretations: (1) There may be, and I think that there almost 
certainly is, a weak acropetal succession, only a few pinnae being formed subsequently 
to, and above those which first appear: to prove this is impossible on a single 
specimen, since the same difficulties arise here as in Cycas Seemanni, and Stangeria, 
and other cases where the number of pinnae is small; (2) It may be that the develop¬ 
ment is really basipetal throughout, but that those pinnae which are nearest to the 
apex develop less strongly than those formed below, but subsequently to them. I 
am unable to give a decided opinion either way, but think the former interpretation 
is by far the more probable. If it were distinctly proved, the case would be an 
interesting one for comparison with Cycas, since it would be the only example among 
those Encephalartece which I have investigated, of even a limited acropetal order of 
succession of the pinnae; moreover, there would thus be added one more character in 
common between Cycas and Dioon. 
Macrozamia Miqueli. 
The material at my disposal consisted of young plants only. These showed on the 
mature leaf a terminal spine, representing the apex of the phyllopodium. It was 
never observed to have developed as a winged structure. On the phyllopodium are 
borne pinnae, usually to the number (in the plants investigated) of about 16 on each 
side : those at the apex of the leaf are usually arranged in equal pairs, though they 
are sometimes irregular. The base of the phyllopodium is as usual developed as a 
