DEVELOPMENT OF PLANTS 361 



divides, forming directly two motionless male gametes during the 

 elongation of the tube, and in other cases the gametes are already 

 formed when the microspores are discharged from their sporan- 

 gia. In none of these cases is there any indication in the division 

 of the antheridial cell of the formation of a wall cell as in the 

 gymnosperms, so that the male gametophyte of the Spermatophyta 

 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 Pinales. 



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 

 the gametospore. In a constantly increasing series of cases the 

 other male gamete has been observed to fuse with the endosperm 

 nucleus, thus making a triple fusion of cells in the formation of 

 this nucleus. While this process is probably in the nature of a 

 reinforcement, enabling the endosperm nucleus to perform its 

 work, it is noteworthy that the qualities of the male parent are 

 transmitted to the endosperm cell just as though this fusion were 

 a sexual process. 



127. The Germination of the Gametospore. — After fertiliza- 

 tion the endosperm nucleus divides repeatedly, and usually the 

 resulting nuclei become arranged about the walls of the sac-like 

 gametophyte which may now be called the embryo sac (Fig. 

 274). Later the endosperm cells develop walls and by further 

 division completely fill the embryo sac with cells. This mass of 

 cells is called the endosperm and the method of its development 

 is exactly similar to that of the female gametophyte of the gym- 

 nosperm, and it serves the same purpose, namely, to nourish the 

 young sporophyte or embryo. Note that it has had an entirely 



