374 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
We may graft on Professor Jeffrey’s arrangement a proposal of 
Professor Lignier’s to associate the Sphenophyllales and Equisetales: 
in the subdivision Articulate. So far, then, as concerns the groups 
which we have to consider in this article our provisional classifica- 
tion may take the following form: 
Sphenophyllales. 
- : Articulate. 
ian eee Equisetales. 
Psilotales. 
Lycopodiales. 
Filicales. 
Pteropsida____{Pteridospermee. ls periephirtas 
Gymnospermee. | 
The Psilotales, though without authentic Paleozoic representatives, 
are included in the list because it is necessary to discuss their affinities 
in the ight of paleontological data, 
The composition of the Vasculares in Paleozoic times was thus 
widely different from what we find in the recent Flora, not only as 
to the groups represented but also as to their relative importance. 
The Pteridophytes and the lower Seed Plants then had the field to 
themselves, and shared among them all the leading roles in the vege- 
table world, filling a place which has since, for the most part, been 
taken over by families of more modern origin. Groups of plants 
which now play a subordinate part, or have disappeared altogether, 
were then richly represented, and in many cases showed a far higher 
and more varied organization than is found among their nearest 
allies in later times. 
In discussing the affinities of Paleozoic vascular plants there are 
certain advantages in beginning with the Sphenophyllales, an order 
which, though not extensive, is important from its synthetic charac- 
ter, and probably represents an extremely ancient stock. 
A. Lycopsipa. 
I. SPHENOPHYLLALES. 
The extinct order Sphenophyllales ranges from the Middle De- 
vonian to the Permian, or perhaps to the base of the Triassic. It 
contains but two genera, Sphenophyllum and Cheirostrobus, each of 
which represents a distinct family, the genus Cheirostrobus being 
known only by its remarkable cones. The species of Sphenophyllum 
were herbaceous, probably climbing plants, with slender ribbed ar- 
ticulated stems, having a triquetrous solid axis of centripetal primary 
