6l6 STRUCTURE AND LIFE HISTORIES 
5. The origin of Cordai tales from Primofilices. 1 
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 
1 The term Primofilices, not . herto used in this text, refers to a hypo- 
thetical, primitive fern stock. 
