193 
Eastern North America), “ the preponderance is equally against 
Western as compared with [astern North America, but is more 
in favor of Europe... so geographical continuity favors the 
extension of identical species; but still Eastern North America 
has more in common with Japan than Western North America 
has.” Gray then enumerates 56 “ peculiar species which Japan 
possesses in common with America, of which 34 inhabit Western, 
and 41 Eastern North America. And 15 are Western and not 
Eastern: 22 Eastern and not Western; and 19 common to both 
sides of the continent.” 
Dr. Gray then notes that the ohne of identical species in 
widely separated districts indicates ‘former continuity, migra- 
tion or interchange, basing his conclusion on Darwin’s (then re- 
cently announced) theory of organic evolution, which teaches that 
individuals of the same kind are descendants from a common 
stock. He then quotes a remark of the botanist Bentham that 
the interchange of the floras of the New World and the western 
part of the Old World suggested “an ancient continuity of terri- 
tory between America and Asia, under a latitude, or at any rate 
with a climate more meridional than would be effected by a junc- 
tion through the chains of the Aleutian and Kurile Islands.” 
Gray then gives his masterful analysis of the problem and his 
conclusion that no such imaginary landbridge as Bentham postu- 
ut that the facts of plant distribution above 
lated 1s necessary, 
noted may be naturally and simply explained by the events pre- 
ceding, during, and following the glacial epoch. In the following 
paragraphs the language, even when quotation marks are not used, 
is largely that of Asa Gray. 
The climatic and other conditions in the geological age immedi- 
ately preceding the Ice Age were such that “ the temperate floras 
of America and Asia must then have been conterminous, and 
therefore have commingled, as conterminous floras of similar cli- 
mate everywhere do.” 
As the glacial epoch came slowly on, carrying glacial ice and 
arctic climate down nearly to the latitude of Ohio, the change 
2 Darwin's Origin of Species (Nov. 24, 1859) had not been published when 
Gray wrote this. He cites the now famous preliminary papers of Darwin 
and Wallace, “ On the tendency of species to form varieties,” etc. Pro- 
ceedings, Linnean Society. Vol. III (Zoology): p. 45, 1858. 
