SPERMATOPHYTES 



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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 nuqleus). 



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 

 they form a very active tis- 

 sue. In the last case, the 

 activity is shown either by 

 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 



Figs. 592, 593. — Development of female ga- 

 metophyte of angiosperms, continued from fig. 591: 

 592, third division, resulting in four nuclei in each 

 end of the sac; 593, organization of egg apparatus 

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

 sac), and antipodal nuclei (base of sac). 



