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. 
Fig. 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. B, an enlarged pollen grain; much magnified. (’, the tip of a pollen tube 
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 odspore; the other disappears. These male cells would be 
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. 
