part 2] pliocene floras. 161 



Eastern United States, the Author stated that she had not been 

 able to trace this regional relationship in the Pliocene of Western 

 Europe. The relationship appeared to be as close with the flora 

 of the Western, as with that of the Eastern United States. She 

 thought it possible that the regional alliance spoken of by Asa 

 Gray might, in part, be due to extermination of species on the 

 great plains of the United States during subsequent Pleistocene 

 migrations, when the change of climate from cold to warmth 

 was fairly rapid, and might have overtaken the rate of travel of 

 the migrating flora. 



