6l6 STRUCTURE AND LIFE HISTORIES 



5. The origin of Cordaitales from Primofilices.^ 



6. The origin of Coniferales from Cordaitales. 



An ancestral tree embodying these views is shown in 



Fig- 433- 



What was the origin of the Primofilices? Here, as 

 often in every science, we have to acknowledge that 

 we do not know; the group is a hypothetical one, 

 and some investigators doubt its actual existence 

 altogether. 



528. Other Views. — (a) Other and equally competent 

 students of the problem take exception to one or more 

 of the six points tabulated above. Not all of their views 

 can here be discussed, but mention may be made of 

 that first elaborated by Jeffrey, of Harvard University. 

 According to this view vascular plants appear at the 

 beginning of the fossil record as two distinct series, the 

 Lycopsida and Pteropsida. The Lycopsida, like the 

 modern Lycopodiales, are characterized by the possession 

 of small leaves (a primitve character), and by few spor- 

 angia on the upper surface of the leaves. The Pteropsida, 

 by contrast, are distinguished, like the modern Filicales, 

 by large leaves, having the numerous sporangia on the 

 lower surface. The two groups also have well-marked 

 anatomical differences. The Lycopsida reached their 

 greatest development in the Paleozoic period, and now 

 appear to be on their way to extinction. The Pteropsida, 

 on the other hand, although possessing many repre- 

 sentatives in former geological ages, still maintain 

 their full vigor, and are considered by this school of 

 paleobotanists to be in the direct ancestral line of our 



^ The term PrimojiUces, not hitherto used in this text, refers to a liypo- 

 thetical, primitive fern stock. 



