376 



GYMNOSPERMS 



the center until the gametophyte is cellular throughout. Even before 

 the gametophyte is completely cellular, there is a difTerentiation into 

 an upper reproductive region, consisting of large elongated cells, and 

 a lower nutritive region, with small cells (figs. 355 and 356). Later, 

 the lower part is further differentiated into an upper storage region, 

 below which the cells act as a haustorium (fig. 355 //, 5). 



Fig. 357. — Ephedra trijitrca: development of male gametophyte: /)and/>r i, first pro- 

 thallial cell; pr 2, second prothallial cell; ai, antheridial initial; /«, tube nucleus; g, gen- 

 erative cell; bn, nucleus of body cell; sin, nucleus of stalk cell; X 1,500. — After Land."* 



Usually there are two archegonia, occasionally only one, and rarely 

 three. The archegonial initial soon cuts ofif a neck cell, which divides 

 several times, forming four or five tiers, before any anticlines appear 

 (fig. 360). As many as eight tiers were observed, and since each 

 divides anticlinally into four or more cells, there are seldom less 

 than 32 neck cells, and often more. Some of the divisions are so 

 irregular that the neck is not sharply marked off from the surround- 

 ing cells (fig. 7,60 C). 



