422 



GYMNOSPERMS 



fertilization. This tissue is shown in Lotsy's figure (391) and in 

 Thompson's figure (395 C). Coulter's figure (393) shows too 

 young a stage to have the antipodal tissue organized. A later stage 

 which, unfortunately, his material did not contain, would have 

 shown antipodal tissue and the pavement tissue. 



Fig. 393. — Gnetum gnemon: A, ovule showing position of female gametophyte and 

 pavement tissue; B, detail of female gametophyte in free nuclear stage, with the nu- 

 tritive pavement tissue beneath; A, Xs4; 5, X300. — After Coulter.''** 



Qualitatively, this gametophyte has nearly reached the angio- 

 sperm level. Although the free nuclear stage is much more extensive 

 than in any angiospcrm, it is still in this stage at the time of fertiliza- 

 tion. There is no archegonium, or even the archegonium initial, 

 which is still retained in Welwilschia. Gnetum has reached the final 

 stage in the reduction of the archegonium. Phylogenetically, neck 

 cells and ventral canal cells are gametes and, in the bryophytes, may 

 possilily function as such. In the heterosporous pteridophytes the 



