I40 DAVID WHITE 



greater, in general, is its value as evidence either for identity of 

 environment or for altered conditions. It must be admitted, however, 

 that in the interpretation of the environmental criteria afforded by 

 fossil plants, relatively little serious study has been given to anything 

 other than climate. The ecology of the fossil floras is a new and 

 almost unexplored department of paleobotany, though splendid 

 work along certain lines was begun by Grand' Eury, The results 

 of differences in soils or in altitude have received little attention. In 

 general the conditions of fossilization naturally presuppose the origin 

 of the vegetal forms at an elevation not far from that of the water- 

 level beneath which they have, in most cases, been preserved, though 

 here and there certain types have been regarded as drifted from higher 

 altitudes. 



THE DEVONIAN FLORAS 



Probable origin of land flora in Devonian. — From the paleobotanical 

 standpoint no period within the existence of land floras is of such 

 imminent interest and yet is so little known as the Devonian. This 

 fact is no doubt due mainly to the relative rareness of indubitably 

 botanical material, its usually fragmentary condition, or its partial 

 obliteration through metamorphism. Yet the Devonian period prob- 

 ably covers the early development, if not the actual beginning, of 

 terrestrial plant life on the earth. It witnessed the origin of ferns, 

 scouring rushes, Lycopods, and Gymnosperms, including the earliest 

 relatives of the conifers. It is supposed to have given birth to the 

 Pteridosperms, a group of seed-bearing ferns (Cycadofices), standing 

 in the gap between the ferns and the Cycads. 



Features of early land plants. — The development in early Devonian 

 time of flat land surfaces and low coasts whose bays were bordered 

 by broad marshes intermittently covered by brackish or fresh waters 

 was most favorable for the nearly simultaneous development of a 

 terrestrial habit in some of the highly varied types which then popu- 

 lated the seas. On some accounts it seems permissible to suppose 

 that the ancestors of the land plants were amphibious, perhaps 

 growing where exposed only at the recession of the tide. It is, I 

 believe, probable that these early plants were but sparsely foliate, 

 their leaves being either spinoid or very small, slender, and delicately 

 thin. The latter were probably dorsally rolled at first during the 



