90 ANNALS NEW YORK ACADEMY OF SCIENCES 



The Oangamopteris flora was already well defined in the early Per- 

 mian. It has no close antecedent types in either the northern or the 

 southern hemisphere, but its actual origin must have antedated the 

 oldest formations where it is known to exist. It may well have been 

 these ancestral types (like the highland fishes of Brazil) which were dis- 

 tributed and not each individual species. These antecedent types may 

 have arisen from the northern cosmopolitan flora and later have migrated 

 into the southern hemisphere where this ancestral stock of the different 

 groups underwent similar evolution in the similar environments of the 

 Gondwana Land. This view is supported by the fact that these ancestral 

 forms would not have necessitated a homogeneous environment, because 

 they were more generalized forms. 



Two objections may be raised against this view. First, it is conceiv- 

 able that Gangamopteris or various individual genera may have origi- 

 nated independently in different continents or in different parts of the 

 same continent, but the assumption that a flora of characteristic asso- 

 ciation and unity as the gangamopterid originated in this way is highly 

 improbable. It is not so improbable, however, if we include representa- 

 tive types of each group in the distributed stock and if we grant, as the 

 facts indicate, that identical evolution took place in similar environments. 



Secondly, there is no fossil record of the gangamopterids in North 

 America. This objection to either a northern origin or a distribution of 

 the ancestral genera by the way of North America is, I believe, far from 

 being a fatal one. If the progenitors of the gangamopterids passed 

 through North America, the line of migration may have been along the 

 Appalachian system during the Carboniferous epoch, but the line of 

 migration was more probably from eastern Asia by way of Alaska. At 

 that time, the necessary Gondwana environment for the Gangamopteris 

 flora may have existed in North America for a brief period. If it did 

 not, we ' only have to assume that the progenitors of this flora did not 

 necessitate Gondwana environments for a ready distribution. Dr. White 

 has told me that there is a little evidence in favor of a Cordilleran 

 migration, and recent work in the Permian of Texas indicates the same. 



The flora would not have required a vast period of time to inter- 

 change between Eurasia by way of North America into South America. 

 The chances are that no trace of these typical Gondwana environments 

 or the ancestors of its flora would remain in either the Appalachian or 

 the Cordilleran regions, because they have been leveled to the sea, except- 

 ing in small patches, and re-elevated several times since that epoch. If 

 the flora was a highland flora, Ave now know where to look for it in 

 western North America. 



