No. 430.] THE EMBRYO SAC OF ANGIOSPERMS. 785 
enormous nuclei, lies at the base of the endosperm and is 
sharply separated from the small-celled endosperm in the upper 
part of the embryo sac. It is probable that the basal group of 
large cells is the product of the lower of the two nuclei derived 
from the first division of the endosperm nucleus. 
In the genus Peperomia the very large endosperm nucleus 
is the result of the fusion of several (usually eight) nuclei. 
It then divides to form the rudimentary endosperm found in 
the ripe seed. 
DOUBLE FERTILIZATION. 
Much interest has been aroused by the discovery of the 
so-called double fertilization which has been demonstrated for 
a large number of angiosperms. This double fertilization con- 
sists in the fusion of the second generative nucleus of the pollen 
spore with the endosperm nucleus, which thus becomes the 
product of three nuclei. This has led to a theory that the endo- 
sperm nucleus is sexual in its nature, and the endosperm arising 
from it is an embryo. That this view can hardly be maintained 
is evident from the condition found in Peperomia, which pre- 
sumably represents a more primitive condition than that of 
the typical angiosperms. In Peperomia, as already stated, the 
endosperm nucleus is the product of several similar nuclei, and 
as such a multiple fusion of sexual cells is quite unknown else- 
where, it is safe to assume that this fusion is not of the nature 
of a true fertilization. 
That the second generative nucleus discharged into the 
cavity of the embryo sac should fuse with the only available 
nucleus, the endosperm nucleus, is not surprising. That its 
character is impressed upon the resulting nuclei is also to be 
expected. This is shown most clearly in the case of hybrid 
maize. It has been clearly demonstrated that one type of maize 
pollinated with another will produce ears in which the endo- 
sperm of the grains shows a hybrid character, due presumably 
to the fusion of one of the pollen nuclei with the endosperm 
nucleus.! 
1 Webber. Xenia, or the Immediate Effect of Pollen in Maize. U.S. Department 
of Agriculture, Division of Vegetable Physiology and Pathology, Bulletin Av. 22, 1900. 
