WHITE PINE 



103 



Fertilization. The tip of the pollen tube breaks and one 

 of the sperms, which has been carried by the tube to the 

 venter, unites with an egg nucleus to form the oosperm. 



FIG. 59. Gymnospermce. White pine. The upper left figure is a micro- 

 sporangium or stamen of white pine showing one cavity filled with pollen 

 grains and one free, of pollen grains. The upper right figure is a cross-section 

 of the stamen with numerous pollen grains. The lower left figure is a longi- 

 tudinal section of an ovuliferous scale with ovule and outer scale. The lower 

 right figure is a longitudinal section of an ovule showing the outer opening 

 or micropyle, the space beneath or pollen chamber, the nucellus and the 

 megasporangium with a large megaspore. 



