130 Sahni. — On Certain Archaic Features in the Seed of Taxus 
appears, however, to fail in this respect, namely, that, so far as is known, 
the ‘ aril * was entirely unrepresented in the Cordaitales. But it is difficult 
to estimate the value of negative evidence, for, apart from the question of 
preservation, these fossil seeds are nearly always found detached, and the 
possibility is not excluded that if an aril was present it was left behind on 
the seminiferous axis when the seed was shed. At least in one of the few 
known cases where the attachment is preserved — namely, Cordaianthus 
Williamsoni — Renault’s well-known figure (see Scott, 1909 , p. 540) shows 
below the seed a differentiated pad of tissue terminating the seminiferous 
axis. May we regard this pad of tissue as the forerunner of an aril ? Since 
I have not seen the original specimen this suggestion must be regarded as 
of the most tentative nature ; but if the aril of Taxus is in origin a disc-like 
expansion of the apex of the seminiferous axis — and this view, held by 
Strasburger in 1872, is perhaps more plausible than any other 1 — it is 
natural to expect that in such an ancient type as Cardiocarpus the aril 
would not be well differentiated from the rest of the axis. It would seem 
as if this disc, as it gradually became differentiated into a distinct organ, 
was in time completely appropriated by the seed, and was shed along with 
it as in Taxus. 
Strasburger long ago ( 1879 , p. 124) expressed the view that the seeds 
of Gymnosperms are often more or less deeply sunk into the seminiferous 
axis, so that it is no longer possible to define their real limits. This view 
found a remarkable illustration when Professor Oliver described the main 
features in the development of the seed of Torreya , and published his 
ingenious interpretation of this peculiar type of seed. In this genus that 
part of the seed which lies below the level of the ‘ chalazal foramina ’ in the 
stone is, according to Professor Oliver, phylogenetically younger than the 
apical region, which (in a figurative sense) may be described as having 
bulged downwards, through the widened seed-base, into a kind of £ brood- 
pouch ’ formed by what is strictly speaking the apex of the seminiferous 
axis. This expanded apex of the axis has, however, been so completely 
monopolized by the encroaching seed that it is now, to all appearance, an 
integral part of the integument ; distally it is continued into the free part 
of the aril, which has had a similar origin at an earlier period, as suggested 
above in the case of Taxus. 
If we keep in view this tendency on the part of the seed to bury itself 
deeper and deeper into the seminiferous axis, the seed of Cephalotaxus 
would appear to have gone even farther than that of Torreya , for the free 
portion of the nucellus which belongs to the archisperm (or phylogenetically 
older part of the seed) is in Cephalotaxus actually arched over by an 
1 Since Ginkgo is traceable to the same source as the Taxales, it is probable that the ‘collar’ of 
this genus is morphologically ot the same origin as the ‘aril’ of Taxus. Sprecher (1907) actually 
employs the term ‘ aril ’ in describing the collar of Ginkgo. 
