io8 FECUNDATION OF FERTILIZATION 



growth down into the female gametophyte can only be accounted 

 for by some chemical stimulus that is located in the ovule and, 

 female gametophyte. A similar attraction brings about a move- 



FIG. 79. Germination of the microspore : A, mature microspore. B, first 

 stage in its germination t, tube cell ; a, antheridial cell. C, end of cell 

 division t, tube cell; a, antheridial cell forming two male gametes. D, 

 diagram showing the formation of the tube which grows through the style 

 and finally reaches the female gametophyte. The two male gametes, g, 

 are shown passing down the tube; t, tube nucleus. 



ment of the cytoplasm which carries the male gametes to the 

 end of the tube cell. It will be seen that this peculiar plant 

 (Fig. 79, D) consisting of a long tubular growth with three 

 naked cells is more rudimentary than the plant derived from the 

 megaspore. Because this plant produces the male cells or male 

 gametes we call it the male gametophyte. So we see that the 

 flower forms two kinds of spores and that these germinate and 

 form two kinds of plants, a male and a female. 



53. Fecundation or Fertilization. As soon as the develop- 

 ment of these two plants is completed a very remarkable change 

 takes place which starts an entirely new growth that is quite 

 independent of the development of the male and female gameto- 

 phyte. The end of the tube cell becomes distended through the 

 accumulation of material and finally ruptures, discharging the 

 male gametes into the female gametophyte. The chemical com- 

 position of the female gamete is such that one of the male cells 

 is attracted to it (Fig. 80) and finally the two gametes unite 



