THE MAIN LINES OF PLANT EVOLUTION 



Stigma 

 Pollen tube (male gametophyte) 



Pollen cell &, 



Sperm nucleus 

 Egg nucleus 



Embryo sac 



Enlarged 

 ovary 



Fruit 



Embryonic sporophyte 



Figure 42. The Life Cycle of a Flowering Plant. (From Young, Hylander, and 

 Stebbins, "The Human Organism and the World of Life," Harper Brothers, 1938.) 



123 



