56 MORPHOLOGY OF REPRODUCTION IN GNETUM. 
Coulter in Gnetum Gnemon also occurs in G. africanum: the latter species 
also shows prefertilization antipodal tissue in the megaspore like that 
described by Lotsy in Gnetum Gnemon, but the existence of which has been 
denied by Coulter. A comparison of Gnetum and Welwitschia leads to the 
statement that the primary endosperms of these two genera are in all respects 
homologous. In an earlier paper the author expressed the opinion that the 
endosperm of Welwitschia is not a true prothallus, but a new structure to be 
regarded as a definite morphological entity, neither sporophytie nor game- 
tophytic, which he designated the trophophyte ; it was further suggested 
that the endosperm of the Angiosperms may be a highly specialised form of 
this trophophyte. The objections raised by Lotsy and other authors to these 
views are fully examined, and evidence is brought forward in support of the 
original contention, The fact that а trophophyte occurs in Gnetum as well 
as in Welwitschia enhances its morphological importance, and the generally 
accepted opinion that Gnetum and Welwitschia are nearer to tho Angiosperms 
than any other Gymnosperms, gives force to the contention that the peculiar 
endosperm of the Angiosperms had its origin in a nutritive tissue not 
essentially different from that in the megaspores of Gnetum and Welwitschia. 
Coulter’s view that there is no necessary phylogenetic significance in its 
nuclear fusion in the embryo-sac of an Angiosperm is also discussed. Tf the 
fusion of nuclei possesses no morphological significance, the phylogeny of the 
nuclei which fuse is still to be determined. Among the very diverse views 
that have been entertained, the possibility that the polar nuclei of Angio- 
sperms may be morphologically, as well as functionally, the representatives of 
the fusing nuclei of Welwitschia and Gnetum has perhaps received too little 
attention. 
