GNETALES 



391 



volume, rather than upon optical sections, which frequently appear 

 to show an inequality that does not exist. 



The male gametophyte of Welwitschia is known only from a few 

 figures by Steasburger (id), 

 which show a prothallial cell and 

 the division resulting in the 

 generative and tube nuclei; 

 supplemented by the statement 

 of Pearson (27) that the nu- 

 cleus of the body cell divides 

 to form two male nuclei. These 

 glimpses agree with the cor- 

 responding stages in Ephedra, 

 except the presence of a single 

 prothallial cell, which may or 

 may not have been accompanied 

 by another one. Our only 

 knowledge of the male gameto- 

 phyte of Gnetum is from the state- 

 ment and figures of Lotsy (15) 

 from Gnetum Gnemon, showing 

 the tube nucleus and two male cells of the ordinary type in the tip of 

 the pollen tube just before fertilization. 



Figs. 442, 443. — Ephedra trifurca: 

 fig. 442, pollen grain just before the for- 

 mation of the tube; the nucleus of the 

 body cell is dividing to form the two male 

 nuclei; Xsoo; fig. 443, the pollen tube; 

 nil and Wa, the male nuclei; s, nucleus of 

 stalk cell; t, tube nucleus; Xsoo. — After 

 Land (23). 



FERTILIZATION 



The fertilization of Ephedra trifurca has been observed by Land 

 (23) and, as has been stated, it may occur within ten hours after 

 pollination. The pollen tube forces its way between the neck cells 

 of the archegonium and discharges all its contents into the cytoplasm 

 of the much elongated egg. While the sperm and egg nuclei are fusing 

 in the upper part of the egg, there may be seen in the overlying cyto- 

 plasm the ventral, second male, stalk, and tube nuclei. A dense and 

 darkly staining mass of cytoplasm surrounds the fusion nucleus and 

 extends downward through the long egg (fig. 444). This differen- 

 tiated mass of cytoplasm appears first in spherical form in the upper 

 third of the central cell, and does not disappear until the proembryonic 

 cells are formed. In Ephedra distachya it is reported (22) that the 



