786 , THE AMERICAN NATURALIST. 
SUMMARY. 
Peperomia, in regard to the embryo sac, probably represents 
the most primitive form yet described among the angiosperms. 
The absence of a definite egg apparatus and antipodals, and 
especially the increased number of nuclei, point to this. The 
single-celled archesporium of Peperomia is, however, probably 
less primitive than the multicellular sporogenous complex 
found in Casuarina and some other forms. 
The similarity between the structure of the embryo sac in 
Peperomia (and perhaps Casuarina) and Gnetum is striking ; 
but as the affinities of the latter are very doubtful, this does 
not throw much light upon the relationships existing between 
gymnosperms and angiosperms. 
The typical embryo sac may very well have been derived 
from one like that of Peperomia, by the suppression of one 
nuclear division. The marked polarity, and the specialization 
of the egg apparatus and antipodal cells, are probably secondary 
characters, and the fusion of the polar nuclei has its prototype 
in the multiple fusion of the nuclei in Peperomia, to form the 
endosperm nucleus. 
Peperomia offers a basis for an explanation of the homolo- 
gies of the embryo sac. The egg cell probably represents an 
archegonium reduced to a single cell, and possibly the synergidze 
may also represent potential archegonia, although it is quite as 
likely that they are derived from vegetative prothallial cells. 
All of the other structures, the polar nuclei (and their product, 
the endosperm nucleus) and the antipodal cells, represent vege 
tative prothallial tissue. The increase in number met with in 
the antipodal cells of Sparganium, for instance, merely empha- 
sizes their power to assume the róle of active prothallial tissue. 
The fusion of the polar nuclei is in no way to be considered 
as a true sexual process. The regular occurrence of a multiple 
fusion in Peperomia is a strong argument against such an 
assumption. It is much more probable that it is to be inter- 
preted as a stimulus to further growth. The fusion of the 
second pollen nucleus with the endosperm nucleus must be 
considered as more or less accidental. 
1 Strasburger. Einige Bemerkungen zur Frage nach der “ doppelten Befruch- 
tung” bei den Angiospermen, Botanische Zeitschrift, 1899. 
