DEVELOPMENT OF PLANTS 



337 



megasporangium has germinated, forming a tube cell and an 

 antheridia cell, but the one or two cells, which correspond to the 

 cell (g) of the gametophyte noted in the cycads, are quickly dis- 

 organized and appear as faint lines (Fig. 254, 8). These cells 

 quickly disappear 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 





8 



FIG. 254. Male gametophyte of the pine : 6, section of microspore, show- 

 ing the two air sacs, s, formed by the lifting up of the outer wall of the 

 spore. 8, stage of germination of the spore at time of discharge from its 

 sporangium t, tube cell; a, antheridial cell, above which are seen two 

 black lines, the remains of ^cells formed by earlier division of the nucleus 

 of the microspore. 9, continuation of germination of the microspore after 

 reaching the megasporangium t, tube cell forming a branching tube that 

 disorganizes and absorbs the cells of the megasporangium. The antheridial 

 cell (a) of 8 has divided into a wall cell, w, and a body cell, b. 10, end of 

 tube cell as it approaches the female gamete m, m, male gametes. The 

 nuclei of the tube cell and wall cell are also seen (somewhat disorganized) 

 in the end of the tube. After Coulter and Chamberlain. 



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 gametes are formed from the body cell. It is 

 23 



