370 MALE GAMETOPHYTE OF FINALES 



cell and an antheridial cell, but the one or two cells, which corre- 

 spond to the cell (g) of the gametophyte noted in the cycads, are 

 quickly disorganized and appear as faint lines (Fig. 254, 8). 

 In some forms several of these prothallial cells are formed so that 

 the male gametophyte is more primitive in this respect than the 

 cycads. On the other hand other groups do not apparently 

 form a prothallial cell at all. So the tendency is towards the 

 elimination of these cells because they are no longer of service 

 in setting free the gametes. The tube cell develops as in the 

 cycads, but it is directed in its growth so that one of its branches 

 finally reaches one of the archegonia, when it pushes aside the , 

 neck cells and fuses with the cell membrane of the large female 

 gamete (Figs. 253, C\ 255, A). In the meantime the antheridial 

 cell has divided into a wall cell and body cell (Fig. 254, 9), and 

 two motionless male cells are formed from the body cell. It is 

 to be noted here that the body cell does not divide, forming cells 

 in which male gametes are organized, as in all preceding cases. 

 It forms two free nuclei and these with their associated cytoplasm 

 function as gametes. It is now apparent why the tube cell 

 extends to the female gamete and also why the archegonial 

 chamber is not developed. The male gametes and the wall cell, 

 now quite unattached, are carried down to the end of the tube 

 (Fig. 254, 10) by the cytoplasmic currents and pass into the cyto- 

 plasm of the female gamete through an opening that is formed 

 in the end of the tube. Chemical attraction now draws one of 

 the male gametes to the nucleus of the female and their fusion 

 results in the formation of the gametospore. The remaining 

 cells of the male gametophyte are apparently disorganized 

 (Fig. 255, A). Several instances have been reported where the 

 male cells differ in size, indicating the loss of function in one of 

 these cells. On the other hand in those groups where the 

 archegonia are closely associated and where, therefore, the tube 

 cell may spread over more than one archegonium, no such reduc- 

 tion appears. The functions performed by the tube cells in the 

 Finales will be a constant characteristic of all the members of 

 the next subdivision or Angiospermae, and it should be noted that 

 this important modification of the male gametophyte probably * 



