390 



GAMETOPHYTE OF AXGIOSPERMS 



vided with walls and consist of a rather larger cell, the female 

 gamete, and two nourishing cells, the synergids or helpers (Fig. 

 271). The inner group or antipodal cells usually have walls and 

 they are either soon disorganized and absorbed by the enlarging 

 gametophyte or they may remain as permanent features of the 

 gametophyte for a long time and even increase greatly in number, 

 serving to nourish the gametophyte by absorbing food from the 

 sporangium. The endosperm nucleus plays a very important 

 role in the development of the sporophyte, for as soon as fertiliza- 



B 



FIG. 270. Germination of the megaspore: A, first division of the mega- 

 spore. B, second division of the nuclei. C, final division of the nuclei. 



tion has been effected it forms by repeated division a mass of cells 

 that completely fills the entire space within the enlarging spore, 

 thus providing food for the nourishment of the sporophyte. At 

 first sight it would appear impossible to compare the various cells 

 of this peculiar gametophyte with the tissues of the female gam- 

 etophyte of the gymnosperms or ferns. It has been suggested 

 that the female gamete and the synergids are the remains of three 

 archegonia, only one of which is usually capable of being fertilized, 

 and that the antipodal cells are a remnant of the numerous vege- 

 tative cells of the gametophyte. The peculiar formation of the 

 endosperm nucleus through the fusion of the two polar cells is 

 looked upon as a nourishing device to give the endosperm nucleus 



