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 



, . FIGS. 592, 593. Development of female ga- 



persistent ; and in some cases metophyte 9 of angio sperms, continued from fig. S9 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 

 A . ., . , . , , (upper end of sac), fusion of polar nuclei (center of 



activity is shown either by sac)> and antipodal nuclei (base O f 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 



593 



