THE GYMNOSPERMS 



36S 



other becomes a sperm mother cell, called the generative cell or 

 the body cell. These cells move along in the apex of the tube. 



The pollen tube rests in 

 the nucellus during win- 

 ter. The following spring 

 it begins growth again, 

 and the nucleus of the 

 generative, or body, cell 

 divides into two sperm 

 nuclei in the one cell. 

 The female prothallium 



Fig. 357- 



Pollen grains of pine, one of them germinating. 

 p 1 and p 2 , the two disintegrated prothallial cells = 

 sterile part of male gametophyte; a.c., central cell of an- m 

 theridium; v.n., vegetative nucleus or tube nucleus of 

 the single-wall cell of antheridium; s.g., starch gi 



; 

 lb 



crnrp 

 S P re 



lus), and when the egg 

 cases are mature the pol- 



Fig. 358. 



Section of nucellus and endosperm of 

 white pine. The inner layer of cells 

 of the integument shown just outside of 

 nucleus; arch, archegonium; en, egg nu- 

 cleus. In the nucellar cap are shown 

 three pollen tubes : vn, vegetative nucleus 

 or tube nucleus; sic, stalk cell; spn, sperm 

 nuclei (the larger one in advance is the 

 one which unites with the egg nucleus). 

 The archegonia are in the endosperm or 

 female gametophyte. (After Ferguson.) 



Fig. 359- 



Archegonium of white pine at stage of fertili- 

 zation, en, egg nucleus; spn, sperm nucleus in 

 conjugation with it; nb, nutritive bodies in 

 cytoplasm of large egg; cpt, cavity of pollen 

 tube; vn, vegetative nucleus or tube nucleus; 

 sc, stalk cell; spn, second sperm nucleus; pr, 

 portion of prothallium or endosperm; sg, starch 

 grains in pollen tube. The sheath of jacket 

 cells of the archegonium is not shown. (After 

 Ferguson.) 



