SPEKMATOPHYTA 



361 



male nuclei directly from the generative nucleus (except in Ephedra), and 

 the presence of compound strobili with simple strobili ("flowers") bear- 

 ing a "perianth." Such strobili suggest the inflorescences of certain 

 angiosperms. The origin of the Gnetales is unknown. They are not 



Fig. 308. Proembryonal cells of Ephedra trifurca, X440. A, three of the eight free 

 proembryonal cells; B, a proembryonal cell in which the embryo initial cell (e) is differ- 

 entiated from the suspensor cell (s). {After Land.) 



closely related to any of the other gymnosperms, while any direct relation- 

 ship to the angiosperms is very doubtful, although both groups may have 

 had a common ancestry. The three genera do not seem to be closely 

 related to one another and may have had a separate origin. Ephedra 

 shows certain resemblances to the Cordaitales that suggest its derivation 

 from that group. 



