Gnetum africanum , with Notes on Gnetum sccindens. 1129 
The closed upper portion of the micropylar tube in Gnetum is similar 
to the part of the tube which Lignier describes as closed in Bennettites , but 
it is not at first sight easy to see how below this the nucellar beak, which, it 
is suggested, represents the closing tissue, could have become so sharply 
separated off as an individual organ, as it is in Lignier’s figures, apparently 
surrounded by a distinct epidermis of its own. Miss Berridge drew my atten¬ 
tion to a point in some of my series of slides of G. africanum which affords a 
possible explanation of this difficulty. In Fig. 9, Pl. LXXXVI, a transverse 
section through the lower part of the closed region of the tube, the closing 
tissue derived from the original epidermis of the tube forms a solid cylinder 
of lignified cells which is separated off from the rest of the tube by the still 
intact and regular subepidermal layer. It would only be necessary for 
this delicate layer to be split off from the central rod in order to get the 
effect shown in Lignier’s Fig. 32, PI. Ill, a solid rod enclosed by the hollow 
micropylar tube. 
In the absence of more perfectly preserved material of B. Morierei , we 
cannot regard this theory of the nucellar beak as proved, but in view on the 
one hand of the other resemblances between the seed and that of Gnetum , 
and on the other of Wieland’s account of the young Cycadeoidea without 
a nucellar beak, it must be regarded, at any rate, as a brilliant hypothesis 
which has every appearance of probability. 
(iii) The structures surrounding and protecting the ovule in Gnetum 
and Bennettites may be compared. It will be seen that while the ovule in 
the latter is enclosed at the base by the ‘ coque ’ or basal husk, this extends 
upwards only for a short distance, and it is the interseminal scales, with 
which the whole is surrounded, that give the ovule efficient protection. On 
the other hand, the interovular portions of the nodal cushion in Gnetum , 
which completely protect the young ovule, and in transverse sections of the 
axis remind one forcibly of the interseminal scales in Bennettites i do not 
continue to enlarge with its growth; and it is the extra outer covering, 
comparable in position with the basal husk in Bennettites , which is the 
efficient protective organ of the mature ovule. It is not necessarily intended 
here to homologize the basal husk with the extra outer covering or the inter¬ 
seminal scales 1 with the projecting portions of the cushion, but physiologically 
the comparison between them has some force. 
The long stalk of G. scandens is suggestive of the long pedicel of the 
Bennettites ovule. Coulter 2 states that there is a short pedicel between the 
s perianth ’ and outer integument in G. Gnemon , but neither Miss Berridge 
nor I have seen any trace of it. 
1 The interseminal scales have already been compared morphologically with the bracts in 
Welwitschia ; Sykes, 1910(1). 
2 Coulter, 1908, p. 381. 
