126 Sargant . — The Reconstruction of a Race of 
and Ernst ( 24 ). The section devoted to the subject in Coulter and 
Chamberlain’s Morphology of Angiosperms ( 19 ) gives a list of references 
up to 1903. In this work, however, the authors express themselves with a 
caution which even in 1903 appeared exaggerated to many morphologists. 
They remark on the wide distribution of the phenomenon, but add : 
‘ Probably it is not safe to infer the general occurrence of double fertiliza- 
tion, although the observations already include sixteen families, about 
forty genera, and over sixty species.’ Sixty species is, of course, a very 
small fraction of the whole number of Angiosperms, but when they represent 
forty genera and sixteen families of very diverse affinities the evidence 
covers a good deal of ground. The strongest point in the case, however, is 
the absence of evidence to the contrary. Excepting apogamous species 
and anomalous cases of that kind, the endosperm has been found to arise 
from such a fusion as Nawaschin described wherever its origin has been 
carefully traced. The partial exception of Peperomia will be discussed later. 
Evidence is still accumulating in the same sense. My list to the end 
of 1907 only reaches seventy-eight species, representing fifty-two genera 
and twenty-two families, but it is no doubt very incomplete. Consider- 
ing the difficulties of observation, even this is a considerable body of 
evidence to be collected in nine years. It justifies botanists in assuming 
that the process of double fertilization is universal among Angiosperms. 
Before considering the views now held on the homology of the endo- 
sperm, it will be convenient to review the facts very briefly. 
The female prothallus of Pteridophytes is formed by the germination 
of the megaspore, and is fully developed at the period when the oosphere is 
formed within the archegonium. 
The female prothallus — the so-called endosperm — of Gymnosperms 
arises by division of the nucleus within the megaspore or embryo-sac. 
Nuclear division is followed after some nuclear generations by cell-division. 
In the majority of cases the embryo-sac is filled with prothallial tissue 
before archegonia appear, and therefore this tissue does not develop further 
after fertilization. 
The female gametophyte is quite clearly defined in both groups : • its 
development begins with the germination of the megaspore and ends with 
the act of fertilization. Moreover, gametophytic tissue cannot be mistaken, 
because the nuclei within it have only half the number of chromosomes 
characteristic of sporophytic tissue. 
The female gametophyte of Angiosperms undoubtedly begins with 
the division of the embryo-sac nucleus, for the embryo-sac is acknowledged 
to represent the megaspore. Three successive mitoses give rise to eight 
nuclei within the embryo-sac— one of them the nucleus of the ovum. So 
far we are no doubt dealing with the gametophyte, yet already — in certain 
genera at any rate — Overton’s test fails us. In these genera the double or 
