THE GYMNOSPERMS 



395 



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. 

 Fig. 371. The female prothallium 



Pollen grains of pine, one of them germinating. fpnHoQnprm^ 



P and A the two disintegrated prothalHal cells = V 611 LOS P ern V 



Sterile part of male gametophyte; a.c., central cell of an- ,' n fU p cnnrp 



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



f antheridium : ^- starch s rains - lus), and when the egg 

 cases are mature the pol- 



sp.fi 



Fig. 372- 



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. 373- 



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.) 



