522 MR. J. PARKIN ON THE 
In the existing Cycads, all dicecious, the male and female sporophylls are 
each separately collected together into cones (stroboli), with one important 
exception, namely, the female sporophylls uf the genus Cycas itself. These 
are borne loosely on the main axis. This continues to grow afterwards, 
producing successions of scale leaves, foliage leaves, and female sporophylls. 
This peculiarity, if one may so call it, of Cycas is of great interest, and may 
be regarded as the retention of an archaic feature possessed by its Pterido- 
spermous ancestors, in which the sporophylls were borne loosely and not 
compacted into cones. 
The cones of Cycads are usually borne solitarilv ; but occasionally they 
may occur in clusters on the apical part of the stem, e. g., frequently in the 
case of the male cones of Zamia, and also in both kinds of cones of 
Encephalartos *. When solitary, there seems little doubt but that the cone 
is in a terminal position ; a lateral bud near the apex then continues the 
vegetative growth, a sympodium being formed f. The cluster of cones 
borne laterally would appear to be a later development, and thus of no 
| great evolutionary significance. 
The strobilus, the homologue of the Angiospermous flower, has then, when 
occurring singly, a terminal position in the Cycads ; at any rate, this would 
seem to be the primitive position. If one imagines a stem of Cycas, after it 
has emitted its first crop of female sporophylls, to cease further elongation, 
a terminal primitive strobilus (* flower ") would result. Further vegetative 
growth would then be taken up by a lateral bud. It is a reasonable 
assumption to conclude that the male sporophylls of Cycas were originally 
borne in a similar fashion to the female ones. The cessation of the further 
growth of the main axis in times past has resulted in the production of 
a male cone or “flower.” Hence the ancestor of the Cycads might be 
looked upon as having unlimited monopodial growth, bearing on its main 
stem successive crops of foliage leaves and sporophylls—in fact, a tree-fern- 
like form with pteridospermous features. 
Taking into account the didecious habit of the Cycads, and the form and 
arrangement of the female sporophylls of Cycas, it would seem that their 
cones must always have been monosporangiate. The unisexual nature of the 
strobilus cannot have arisen through reduction, but must have been due to 
the segregation of one kind of sporophyll into a cone from the Pterido- 
spermous condition. 
It must have been otherwise with the Bennittitean stock. In this group 
the stroboli contained, at least in many forms, both male and female 
sporophylls arranged in a definite manner the one to the other, viz. the 
* Pearson, H. H. W., * Notes on South African Cycads.—I.,” Trans. S. African Phil, 
Soc. xvi. (1906) p. 341. 
T Solms-Laubach, Graf zu, Bot. Zeit. xlviii. (1890) p. 177. 
