378 



GAMETOPHYTE OF ANGIOSPERMS 



gymnosperms, so that the male gametophyte of the Spermato- 

 phyta presents a very regular series of reductions from the cycads 

 to the pines and thence to the angiosperms, where it consists of a 

 tubular growth containing three naked cells (Fig. 272, D). This 

 development of the male gametophyte requires from a day to 

 several months and is quite independent, apparently, of the dis- 

 tance that it has to traverse in reaching the female gametophyte. 

 The male gametes are often somewhat elongated and even spi- 

 rally coiled and carried to the end of the tube, as in the Finales. 



Fig. 273. Section of the micropylar end of the megasporangium, show- 

 ing the process of fertilization. The tube, t, has passed through the micro- 

 pyle, entered the female gametophyte and ruptured, discharging the male 

 gametes. One, cf , is shown fusing with the female gamete, 9 , and the other 

 one, cf' , is uniting with the two polar nuclei, thus making a triple fusion in 

 the formation of the endosperm nucleus; s, one of the synergids;i, integu- 

 ments. 



126. Fertilization. — The end of the tube finally ruptures, owing 

 to the tension of the fluids that gradually accumulate in it, and 

 the male gametes are forcibly expelled into the sac-like cavity 

 of the female gametophyte (Fig. 273). One of the male gametes 

 passes over to and fuses with the female gamete, thus forming 



