THE SEED PLANTS 



291 



known as the pollen tube. While the tube is developing, its 

 contents divide and produce several cells, two of which are 

 male cells (fig. 225). The tube makes its way to the egg, and 

 when it arrives, its tip opens and the two male cells pass out. 



Fio. 225. Stamens, pollen, and pollen tube of the pine 



A, a few of the stamens and pollen sacs from a staminate cone ; somewhat mag- 

 nified. /.'. an enlarged pollen grain ; much magnified. C, the tip of a pollen tuhe 

 at the time when it has almost reached the egg ; just back of the two nourishing 

 cells are the two darkly colored male cells, either of which may fertilize an egg ; 

 much magnified 



Either of the male cells may unite with the egg to produce 

 an oospore ; the other disappears. These male cells would l>e 

 called sperms if they had cilia, but they have not. There are 

 a few gymnosperms (the older ones most resembling the ferns) 

 in which the male cells have cilia, can swim actively, and are 

 true sperms, but even these are carried by the pollen tube. 



