74 



PLANTS AND MAN 



which grows down through the pistil to its enlarged base (the 

 ovary) where the ovule is located (fig. 48) ; this takes from a few 

 hours to several months, varying with the different types of 

 flowers. Once the pollen tube has reached the vicinity of the ^^g, 

 a male nucleus moves down through the tube, unites with the 

 Qg'g, and fertilization takes place. At this point, a new sporophyte 

 generation has come into existence. 



MALE 



GAMETOPHTTE 



FEMALE 

 GAMETOPHYTE 



OVULE 



Fig. 48. — Diagram of pollination and development of the gametophytes. 



In the meantime, superficially the apple blossom looks as if 

 nothing has taken place. All the stages intervening between pol- 

 lination and fertilization take place in the pistil, involving hidden 

 microscopic male and female prothalli; the sexual generations 

 have been reduced to degenerate parasites living within the 

 reproductive organs of the sporophyte. But after fertilization, 

 changes take place in the flower. The petals wither and fall off", 

 having played their role in reproduction. The fertilized ^^^%, 

 remaining in place, grows into an embryo with three well- 



