REPRODUCTION: ALTERNATION OF GENERATIONS 275 



that produced it, or after it has been carried to the pistil. 

 The growth of the pollen, as well as its resemblance to the 

 gametophyte, is so slight that 

 it was not recognized for years 

 after plants had been carefully 

 studied But it is now known 

 that the pollen does, at least 

 in some of the higher plants, 

 develop sufficiently to show the 

 gametophyte stage and then 

 produces what corresponds to 

 antheridia; Fig. 128 g. The 

 pollen tube which grows down 

 through the style of the pistil 

 (Figs. 65 and 127 pi), in a way 

 corresponds to the antheridium; 

 and inside it are small cells, or 

 nuclei of cells, ra, that corre- 

 spond to and have thesame func- 

 tion as sperms. In other words, 

 the pollen does not correspond 

 to a sperm, but is simply a spore 

 that grows into a male gameto- 

 phyte, which itself produces the 

 equivalent of sperms. 



It is thus seen that inside 

 of the pistil one kind of spore 



grows into a female gametophyte and produces eggs, while on 

 the stigma the other kind of spore grows into a rudimentary 

 male gametophyte and produces the equivalents of sperms. 



Following farther the comparison with a fern, the next step 

 is the fertilization of the egg of the female gametophyte by 

 the sperm of the male gametophyte. In the flower this fusion 

 is accomplished as follows: The pollen tube (Fig. 128 E) is an 

 outgrowth from the male gametophyte, and pushes its way 



FIG. 127. A SECTION OP AN 



OVULE AFTER THE SPORE HAS 

 GROWN INTO THE FEMALE GAME- 

 TOPHYTE 



G, the gametophyte; e, egg; pt, a pollen 

 tube pushing its way through the style to 

 fertilize the egg; ra, is the male nucleus in 

 the pollen which corresponds to the sperm 

 and fertilizes the egg. 



