104 



GYMNOSPERMS 



This union of the sperm and egg nucleus is called fertilization. 

 Several egg cells may be fertilized but only one usually 

 develops. 



FIG. 60. A. While pine: 1, Pollen grain with nucleus; 2, nucleus di- 

 vided into two cells; 3, the two cells divided into two upper prothalial cells 

 and a generative and tube cell; 4, one prothalial cell has disappeared and 

 the protoplasm has increased in amount; 5, pollen tube is forming; 6, the 

 generative cell has divided into a stalk cell and an antheridial cell; 7-8, the 

 pollen tube is elongating and the antheridial cell has passed into the tube; 

 9, the long pollen tube contains the tube nucleus, the two sperms and the 

 stalk cell nucleus. 



B. Female Gametophyte. 1. Embryo sac; 2, archegonium; 3, neck cells; 

 4, egg cell. 



