312 MORPHOLOGY OF GYMNOSPERMS 



involving as it does the question of the relationship of Cordaitales 

 and Cycadofilicales. It is evident, therefore, that Cycadales and 

 Coniferales are as far apart as the history of gymnosperms could 

 make them. The connection of Pinaceae and Ginkgoales is much 

 closer, for it is evidently made through their common ancestral group, 

 the Cordaitales. These two groups, therefore, have many characters 

 in common, but have carried forward differences that have made them 

 distinctly divergent, and they are now as far apart as two groups with 

 an immediate common ancestry can be. The relation of Pinaceae 

 to Taxaceae is obscure, but the combined testimony of history and of 

 structure suggests that the latter have been derived from the former. 

 A fuller discussion of this is deferred until the Taxaceae are presented. 

 The relation of Pinaceae to Gnetales is still more obscure, but a phylo- 

 genetic connection seems evident through Ephedra, which will be 

 considered later.' 



I The literature cited for Pinaceae will be found under the general list for Conif- 

 erales, at the end of the next chapter. 



