SPERMATOPHYTES 
265 
feature referred to is the polar fusion, which means that a nucleus from 
each end passes toward the center of the sac, where the two come into 
contact and fuse (figs. 593, 594), forming the fusion nucleus (primary 
endosperm nucleus). 
Egg apparatus and antipodals. The three nuclei in the micropylar 
end of the sac are organized into a group of three naked cells called the 
egg apparatus (figs. 593, 594). 
The cells are all potential 
eggs, but only one of them 
(the central one) matures as 
a functional egg. The other 
two are called synergids 
(helpers), because they are 
apparently of some service 
in connection with fertiliza- 
tion. Often the synergids 
become beaked, the beaks 
sometimes even extending 
into the micropyle. The 
three nuclei at the antipodal 
end of the sac form a group 
of three naked cells or walled 
cells, called antipodal cells 
(figs. 593, 594), or merely 
antipodals, and their his- 
tory is exceedingly variable. 
Usually they are ephemeral; 
sometimes they are quite 
persistent ; and in some cases metophyte of ang i osper m Sl continued from fig. 59 i : 
they form a very active tis- 592, third division, resulting in four nuclei in each 
SUe. In the last case, the end of the Sac 5 593, organization of egg apparatus 
. ., . , (upper end of sac), fusion of polar nuclei (center of 
activity is shown either by sJ), and antipodal nuclei (baS e of sac), 
the great enlargement of the 
three cells, or by their division to form a variable amount of tissue. In 
any case, when the antipodals are active, they serve as nutritive cells, 
and in general they serve this purpose until the endosperm is formed. 
Exceptions. The sequence of events described above is remarkably 
uniform for so great a group as the angiosperms; but there are certain 
interesting exceptions. For example, in a member of the pepper family 
592 593 
FIGS. 592, 593. Development of female ga- 
