368 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1932 



ferns, so far as we know, did not play a part in the vegetation until 

 later. 



It is not intended to describe the oldest known terrestrial plants 

 but rather to show by a few examples that, despite the meagerness 

 of the records, it is possible to obtain a glimpse of the vegetation of 

 the world in an age separated from the present by 200 to 300 mil- 

 lions of j^ears. In the course of the latter part of the Devonian 

 period many new types were evolved; woody trees vying in com- 

 plexity of structure with modern conifers, though probably not 

 closely related to them ; plants bearing large fernlike fronds, which, 

 it is suspected, were not true ferns but members of an extinct group, 

 which rose to greater prominence in the forests of the coal age ; trees 

 with forked stems and branches bearing pendulous spore capsules 

 and needlelike leaves resembling the Lepidodendrce and other arbo- 

 rescent Lycopodialean plants of Carboniferous floras. 



Passing to the Carboniferous period we find that the land vegeta- 

 tion had reached a nnich higher level; there were many new types, 

 and the dominant groups Avere represented by an amazing variety 

 of forms. It was in the latter part of the Carboniferous period 

 that the Paleozoic plant world reached its culminating point. Atten- 

 tion is called to one of the extinct groups, the pteridosperms, so 

 named because the large compound fronds closelj'^ resembled those 

 of ferns but differed in bearing seeds and not merely spores. With 

 them were associated some undoubted ferns, some of which differed 

 widely from any that still exist; others already exhibited features 

 characteristic of living ferns. The pteridosperms seem to have 

 occupied a position in the late Paleozoic floras comparable to that 

 now held by the flowering plants; it may be that these two great 

 classes, though distinguished by several important features, are not 

 unrelated. With the pteridosperms Avere associated tall calamites 

 resembling in habit of growth gigantic Equiseta^ though probably 

 not their direct ancestors; Lepidodendron^ /SigiUaria, and other 

 arborescent members of the group Lycopodiales, which includes also 

 the living club mosses and groimd pine {Ly cop odium). In the 

 forests of the Coal Age some of the more abundant and conspicuous 

 trees seem to afford instances of gigantism; it is not clear that they 

 left any direct descendants which persisted to later ages; they were 

 highly differentiated plants which reached their maximum size in 

 the latter part of the Carboniferous period and then gradually passed 

 out of existence. Like the dinosaurs in the animal kingdom they 

 were overdeveloped members of the plant kingdom unfitted to com- 

 pete successfully with later and more efficient products of evolution. 

 In the Carboniferous period there were also smaller, herbaceous 

 lycopods surprisingly simihir to living species of Selaginella which 



