DEVELOPMENT OF PLANTS 



343 



the cell (t) called the tube cell, represents a new departure in 

 the evolution of the male gametophyte. The tube cell grows 

 out into the tissues of the megasporangium forming a tubular 

 structure, often branching extensively, and absorbs food for the 

 nourishment of the antheridial cell (Fig. 247, B). This latter 

 cell finally divides, forming a rudimentary antheridium con- 



FiG. 247. Male gametophyte of Zatnia: A, stage of germination of the 

 microspore attained in the sporangium. See text for explanation of figures. 

 B, formation of tube for absorbing of food from megasporangium. C, spore 

 end of gametophyte showing the antheridial cell dividing into a body cell, 

 h, and a single wall cell, w. D, the body cell has divided, forming two cells, 

 which become the male gametes. E, spore end of male gametophyte, show- 

 ing the spirally ciliated gametes. — After Webber. 



sisting of but a single wall cell (iv) and a body cell (b), which 

 by division forms directly two huge male gametes with spirally 

 arranged cilia (Fig. 247, C-E). Owing to the growth of the 



