CHAPTER XXXVI. 



pollen grain of tril- 

 lium. The sm 



smaller 



cell is the genera- 

 tive cell. the mother cell. 



GAMETOPHYTE AND SPOROPHYTE OF ANGIO- 

 SPERMS. 



650. Male prothallium of angiosperms. The first division 

 which takes place in the nucleus of the pollen grain occurs, in 

 the case of trillium and many others of the angio- 

 sperms, before the pollen grain is mature. In the 

 case of some specimens of T. grandiflorum in 

 which the pollen was formed during the month 

 of October of the year before flowering, the divi- 

 Neariy mature sion of the nucleus into two nuclei took place 

 soon after the formation of the four cells from 

 The nucleus divided in the 

 young pollen grain is shown in fig. 385. After this takes 

 place the wall of the pollen grain becomes stouter, and minute 

 spiny projections are formed. 



651. The larger cell is the vegetative cell 

 of the prothallium, while the smaller one, since 

 it later forms the sperm cells, is the generative 

 cell. This generative cell then corresponds 

 to the central cell of the antheridium, and the 

 vegetative cell perhaps corresponds to a wall 

 cell of the antheridium. If this is so, then the 

 male prothallium of angiosperms has become 

 reduced to a very simple antheridium. The 

 farther growth takes place after fertilization. 

 In some plants the generative cell divides into 

 the two sperm cells at the maturity of the pollen grain, 

 pollen grain. In other cases the generative cell divides in the pollen tube 

 after the germination of the pollen grain. For study of the pollen tube the 

 pollen may be germinated in a weak solution of sugar, or on the cut surface 



325 



(poll 



ided 



egetat 



