374 



GAMETOPHYTE OF ANGIOSPERMS 



the stalk which supports it becomes curved so that it very fre- 

 quently is turned completely over (Fig. 269, B). The germina- 

 tion of the megaspore results in a female gametophyte which is 

 very much more reduced than in the case of the gymnosperms. 

 As the megaspore enlarges, disorganizing the cells of the sporan- 

 gium, also called the nucellus, its nucleus divides and the daugh- 

 ter nuclei move to each end of the spore (Fig. 270, A). Each 

 of these nuclei divides twice, forming four nuclei at either end 

 of the spore (Fig. 270, B, C). A nucleus from each of these 



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. 



groups, called the polar nuclei, now approach each other and fuse, 

 forming a single large nucleus that is usually called the endo- 

 sperm nucleus. This rudimentary growth represents the female 

 gametophyte. The three outer or micropylar cells are not pro- 

 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 



