i 
GEOGRAPHIC DISTRIBUTION OF LIFE IN NORTH AMERICA. 403 
The above table shows, so far as the genera of mammals and birds 
are concerned, that the difference between the humid “Atlantic” or 
“Eastern province” on the one hand, and the arid Great Plains and 
Great Basin on the other, is less than one-fourth as great as the differ- 
ence between the Sonoran and Boreal regions. 
These facts, it seems to me, should suffice to establish beyond dispute 
the subordinate part played by humidity in comparison to temperature, 
and should dispe! any lingering doubts that may still haunt the minds 
of conservative naturalists respecting the necessity of abandoning the 
long accepted division of the United States into Atlantic, Central, and 
Pacific provinces. 
REMARKS CONCERNING SOME OF WALLACE’S STATEMENTS. 
Wallace, in his great work on geographic distribution, and in sub- 
sequent writings on the same subject, greatly under-rates the impor- 
tance of temperature as a factor in determining the distribution of life. 
He lays great stress upon the dissimilarity of the faunas and floras of 
parts of Africa, South America, and Australia lying in the same lati- 
tude, and ealls particular attention to the circumstance that although 
the climate may be identical over these widely separated areas, the 
species and higher groups are totally distinct, because the regions have 
been disconnected since early geologic times,—as if these facts were not 
self-evident. On the other hand, in single continental areas where 
there is no break or barrier of any kind between widely different faunal 
zones, he tries to invent some unnatural reason for the differences 
observed, and is reluctant to admit that even in these cases climate or 
climatic conditions can constitute the barriers to dispersion that 
undoubtedly exist. He says of climate: ‘‘ Probably its action is indi- 
rect, and is determined by its influence on vegetation, and by bringing 
diverse groups into competition.” 
In another place he states: ‘“‘Hot countries usually differ widely from 
cold ones in all their organic forms; but the difference is by no means 
constant, nor does it bear any proportion to difference of temperature. 
Between frigid Canada and sub-tropical Florida there are less marked 
differences in the animal productions than between Florida and Cuba 
or Yucatan,so much more alike in climate and so much nearer together.” 
He states further: “‘The eastern United States possess very peculiar 
and interesting plants and animals, the vegetation becoming more Iux- 
uriant as we go south, but not altering in essential character; so that 
when we reach the southern extremity of Florida we still find ourselves 
in the midst of oaks, sumacs, magnolias, vines, and other charac- 
teristic forms of the temperate flora; while the birds, insects, and land- 
shells are almost identical with those found farther north. Butif we 
now cross over the narrow strait, about 50 miles wide, which separates 
Florida from the Bahama Islands, we find ourselves in a totally dif- 
