﻿446 ON THE BOTANY OF JAPAN. 



the considerations which Mr. Darwin first brought to bear upon such questions, and 

 which have been systematically developed and applied by the late Edward Forbes, by 

 Dr. Hooker, and by Alphonse De Candolle. 



No one now supposes that the existing species of plants are of recent creation, or 

 that their present distribution is the result of a few thousand years. Various lines of 

 evidence conspire to show that the time which has elapsed since the close of the 

 tertiary period covers an immense number of years ; and that our existing flora may 

 in part date from the tertiary period itself. It is now generally admitted that about 

 20 per cent of the MoUusca of the middle tertiary (miocene epoch), and 40 per cent 

 of the pliocene species on the Atlantic coast still exist ; and it is altogether probable 

 that as large a portion of the vegetation may be of equal antiquity. From the nature 

 of the case, the direct evidence as respects the flora could not be expected to be equally 

 abundant. Still, although the fossil plants of the tertiary and post-tertiary, of North 

 America have only now begun to be studied, the needful evidence is not wanting. 



On our northwestern coast, in the miocene of Vancouver's Island, among a singular 

 mixture of species referable to SalLv, Pojnihis, .Quercus, Plancra, Diospi/ros, Salishuria, 

 Ficiis, Ciunamommn, Persoonia or other Proteacea, and a Palm (the latter genera 

 decisively indicating a tropical or subtropical climate), Mr. Lesquereux has identified 

 one existing species, a tree characteristic of the same region ten or fifteen degrees 

 farther south, viz. the Redwood or Sequoia sempervirens. In beds at Somerville referred 

 to the lower or middle pliocene by Mr. Lesquereux, this botanist has recently identified 

 the leaves of Persea Carolinensis, Prunus Carolmiana, and Quercus mi/rtifolia, now in- 

 habiting the warm sea-coast and islands of the Southern States.* 



The pliocene quadrupeds of Nebraska also show that the climate east of the Rocky 

 Mountains at this epoch was much warmer than now. About the Upper Missouri and 

 Platte there were then several species of Camel (Procamelus) and allied Ruminantia, 

 and a Rhinoceros, besides a Mastodon, an Elephant, some Horses and their allies, 

 not to mention a corresponding number of carnivorous animals. These herbivora 

 probably fed in a good degree upon herbage and grasses of still existing species. 

 For herbs and grasses are generally capable of enduring much greater climatic changes, 

 and are therefore likely to be even more ancient, than trees. These animals must 

 have had at least a warm-temperate climate to live in : so that in lat. 40° - 43° they 

 could not have been anywhere near the northern limit of the temperate flora of those 



* These and other data, obligingly communicated by Mr. Lesquereux, will be published in the May number 

 of the American Journal of Science and Arts. 



