250 Tra7isactio7is of the Royal Society of South Africa. 
(2) the results of the fusion are entirely different. This question has already 
been dealt with.* 
Systematic writers frequently use as a distinguishing character between 
the Angiosperms and the Gymnosperms, the formation of endosperm before 
fertilisation in the latter, after in the former. In certain species of Grnetum, 
possibly in all, either condition may occur. Here, then, the character is of 
little importance. But in all species of G-netum, as in Welwitschia (and in the 
Angiosperms), the gametes are ahvays constituted before the formation of 
eyidosperm commences. One most outstanding character of the prothallus is 
that it produces the gametes if these are not eliminated from the cycle. If 
both prothallus and gametes are present, the former precedes the latter in 
ontogeny. The characters of the fusion-nuclei also are not those of a 
gametophyte. In a life-history which includes reduction phenomena of a 
normal character, a tissue whose nuclei contain a number of chromosomes 
which is not constant, but always greater than that characteristic of the 
sporophyte, can hardly be regarded as a gametophyte. Therefore to apply 
the term " prothallus " to the endosperm of Gnetum or Welwitschia is, in 
our view, a quite unjustifiable " Spiel mit worten." t 
On the other hand, there appears to be no reasonable ground for regard- 
ing this tissue as a sporophyte. The sperm-nucleus takes no part in its 
formation — it is formed even in ovules which are not pollinated — and there is 
no evidence whatever that it is a monstrous embryo of apogametic origin. 
The number of the fusing nuclei, the number and character of the fusion- 
nuclei and all the circumstances of the fusion are opposed to this view. 
It appears to be more in harmony with the facts to regard the endosperm 
of Gnetum and Welwitschia as a tissue, probably rather an organism, J 
which has been " side-tracked " from the direct line of the life-cycle — a 
" by-product resulting from the fusion of potentially sexual nuclei, and 
functioning in the same manner as the prothallus of the lower seed-plants 
which it replaces in the nutrition of the embryo. § In order to emphasise 
the fact that it is neither a gametophyte nor a sporophyte, it was proposed 
to designate it trophophyte." § In view of the recent additions to our 
knowledge of the life-history of Gnetum, this proposal seems unobjectionable 
so long as there is no implication that the trophophyte is a new " genera- 
tion " intercalated into the life-cycle. Diagrammatically its place in the life- 
cycle may be represented as on the followmwj page. 
There are two marked differences between the endosperms of Gnetum 
and Welwitschia, viz. (1) the septation in Gnetum occurs progressively from 
the base upwards ; in Welwitschia it is practically simultaneous throughout 
^ Pearson, 1915 a, pp. 324-327. 
t Lotsy, 1911, p. 340. 
+ Lotsy, 1899, p. 93. 
§ Pearson, 1909, p. 355. 
