156 WAKE-ROBIN. 



reduced, but in Angiosperms the reduction is greater, 

 the male gametophyte consisting merely of one tube- cell 

 and two male cells. These may form before the mi- 

 crospore has left the microsporangium. 



The megaspore is formed within the nucellus of the 

 ovule as in the Gymnosperms, but its germination differs 

 somewhat. The germination of the megaspore results 

 in the formation of a seven-nucleate female gametophyte 

 consisting of three antipodal nuclei, the primary endo- 

 sperm nucleus, and the egg apparatus consisting of an 

 egg and two synergids. 1 Fertilization of the egg then 

 occurs, forming the oospore. 



The peculiar phenomenon of double fertilization, 

 already proven to exist in many plants and probable 

 for others, offers problems difficult to solve. Heretofore 

 it has been customary to consider the endosperm as a 

 delayed development of the female gametophyte. The 

 phenomenon of double fertilization suggests the possi- 

 bility of two embryos formed within the embryo-sac, 

 the one developing normally into the embryo plantlet, 

 while the other becomes the endosperm and serves to 

 nourish its twin. Further researches may give light 

 upon this question. 



By continuous divisions transverse to the long axis 

 of the embryo-sac, the oospore develops the several- 

 celled suspensor and the cell or cells known as the embryo 

 proper. As the latter grows, various parts are differen- 

 tiated and with the simultaneous growth of the ovule 

 the ripened seed is formed. After a period of rest this 



1 The exact correspondence of these various structures to those in 

 Gyrnnosperms and Pteridophytes has not yet been determined. 



