444 



GYMNOSPERMS 



sperms; but the female gametophytc of Cardiocarpus, assigned to 

 Cordaites, looks like that of Ginkgo. On the basis of similar struc- 

 tures, Ginkgo and Cordaitales are closely related. The megaspore 

 membrane is highly developed in CycadoliHcales, and the gameto- 

 phytes are cellular throughout. 



Fig. 397. — Diagrams indicating the comparative extent of the x and 2X generations 

 in various plants. In the second diagram, the e.xtcnt of the 2x generation is exaggerated; 

 in the sixth and seventh, the x generation is exaggerated. 



The female gametophyte of gymnosperms thus stands between 

 those of the ptcridophytcs and the angiosperms. 



In the alternation of generations the sporophyte of the gymno- 

 sperms has become as dominant as in the angiosperms. The male 



