450 THE AMERICAN NATURALIST [Vol. XLI 



gives one more proof of the wide extension of the same flora, 

 since the Ehnira woods contain an ehn which will be designated 

 as JJ. 'proio-racemosa. 



Biological Considerations 



The present determinations lend emphasis to previous conclu- 

 sions respecting the character of the Den flora, its relation to 

 existing vegetation in the same region, and its indications of the 

 existence of a climate warmer than at present and comparal)le 

 wath that of the middle and southern United States. 



With four exceptions, Ostrva, Gleditschia, Cercis and Acer 

 torontoniensis , the flora indicated by the present studies is identical 

 w'ith that previously determined to be characteristic of the Don 

 Period or Warm Climate Period of the Pleistocene. But an 

 examination of these four new elements, shows that they also, 

 are quite consistent factors in the warm climate flora. 



Gleditschia tricicanihos L. which is undoul^tedlv the nearest living 

 representative of the fossil, finds its northern limit of distribution 

 according to Macoun ('S3), in Ontario, and it occurs on the sand 

 dunes of Pelee Point to which the seeds appear to have been carried 

 across the I^ake from Ohio. But according to Sargent ('Q2, III, 

 75) this species appears on the western slope of the Alleghany 

 Mountains whence it extends westward as far as longitude 96°, and 

 southward to Alabama, Mississippi and tlie Brazos River in Texas, 

 from wdiich it would appear that it is distinctly characteristic of a 

 climate warmer than that now known in the region of Toronto, 

 and comparable with that of the Don Period in Pleistocene time. 



Cercis canadensis is practically unknown in Canada, although 

 Britton ('97, II, 257) records it as occurring in southern Ontario. 

 Sargent on the other hand ('02, III) gives its northern limit as New 

 Jersey, whence it extends southward to Tampa Bay and westward 

 to the Brazos River in Texas. The evidence which it affords of a 

 warm climate is even more conclusive than in the previous case. 



Ostrya mrginica ranges from Cape Breton westward through 

 the Valley of the St. Lawrence to Pake of the Woods and Rat 

 Portage, northern ^Minnesota and the Black Hills of Dakota, and 

 southward to northern Florida and eastern Texas. Although 

 the tree is very common throughout all this region, Sargent ('02, 



