CHAPTER XXXVI. 



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- 

 i-ig. 385. ^ •' ^ &' 



Nearly mature sion of the nucleus into two nuclei took place 



pollen grain of tnl- . . , ,, r 



Hum. 1 he smaller sooii alter the formation 01 the four cells from 



cell is the genera- ,..,,. , 



live cell. the mother cell. 1 lie nucleus divided m 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 corresp'ind? 



to the central cell of the antheridium, and the 



vCL^etative cell perh.ips 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 ""^'='.' vegetative 

 ^ ° cleus in each near 



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



piillen 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 



lermurating 



vided 



