172 
WALTER P. THOMPSON 
origin of "double fertilization" or ''triple fusion" and yet from the 
conditions in Gnetum one may well imagine how the phenomenon 
arose. It should be rem-embered that in the embryo-sac before 
fertilization there are fusion nuclei and a male nucleus in addition 
to the egg and male nucleus which will fuse to form the embryo. 
While I cannot confirm Lotsy's statement that the second male 
nucleus always functions, I have seen one case in which it did function. 
If the second male nucleus fertilized a fusion nucleus in place of an 
egg the typical Angiosperm condition would be reached. Further- 
more it has been shown that in certain of the lower Angiosperms 
double fertilization does not occur. 
We have just concluded that in respect to three of the four im- 
portant differences between the endosperm of Gymnosperms and 
that of Angiosperms, Gnetum resembles the latter. And yet in re- 
gard to each of them we find evident reminiscences of the Gymno- 
sperm condition. It seems, therefore, a reasonable conclusion that 
the endosperm of Gnetum is really the type from which that of Angio- 
sperms has been derived, and that it in turn has been derived from 
the Gymnosperm type. 
Moreover the conditions in Gnetum have a distinct bearing on 
the morphology of the endosperm in Angiosperms. As is well known 
there are two views on this subject: (i) that it is belated gameto- 
phytic tissue and (2) that it is really an embryo rendered monstrous 
by the introduction of the second female nucleus. In Gnetum there 
can be no doubt that it is belated female gametophyte, although 
the fusion of nuclei preceding its initiation is difficult to understand. 
Indeed, although the conditions are much more primitive in Gnetum 
we appear to be no nearer an understanding of the meaning of the 
fusion than we are in the case of Angiosperms. We can only fall 
back on the old idea that it is in the nature of a vegetative stimulus 
to growth. Now in spite of the fertilization of the fusion nucleus by 
the second male nucleus in a great many Angiosperms, the endosperm 
of the latter group is of the same nature as that of Gnetum. This 
is true not only because of the transitions seen in Gnetum but also 
because the triple fusion is not always a prerequisite to endosperm 
formation in Angiosperms. It follows therefore that the endosperm 
of Angiosperms is just as much female gametophyte as is that of 
Gnetum and this would be true whether or not the endosperm of 
Angiosperms had been derived from that of Gnetum. 
