590 SEQUOIA AND ITS HISTORY. 
preceding and perhaps following. I considered that our own 
present vegetation, or its proximate ancestry, must have occupied 
the arctic and subarctic regions in pliocene times, and that it had - 
been gradually pushed southward as the temperature lowered and 
the glaciation advanced, even beyond its present habitation; that 
plants of the same stock and kindred, probably ranging round 
the arctic zone as the present arctic species do, made their forced 
migration southward upon widely different longitudes, and receded 
more or less as the climate grew warmer; that the general differ- 
ence of climate which marks the eastern and the western sides of 
the continents,— the one extreme, the other mean — was 
less even then established, so that the same species and the same 
sorts of species would be likely to secure and retain foothold in — 
the similar climates of Japan and the Atlantic United States, but — 
not in intermediate regions of different distribution of heat and 
moisture; so that different species of the same genus, as in 
Torreya, or different genera of the same group, as redwood, Taxo- 
dium and Glyptostrobus, or different associations of forest trees, 
might establish.themselves each in the region best suited to its 
particular requirements, while they would fail to do so in any other. 
These views implied that the sources of our actual vegetation and - 
the explanation of these peculiarities were to be sought m, 
and presupposed, an ancestry in pliocene or still earlier ue 
occupying the high northern regions. And it was thought that 
the occurrence of peculiarly N orth American genera in Europe ® 
the’ tertiary period (such as Taxodium, Carya, Liquidambar, inal 
safras, Negundo, etc.), might be best explained on the assumption — 
of early interchange and diffusion through North Asia, rather tha 
by that of the fabled Atlantis. as in 
The hypothesis supposed a gradual modification of species ae 
different directions under altering conditions, at least to ™ 
extent of producing varieties, subspecies and pre singe 
species, as they may be variously regarded ; likewise 
and local origination of each type, which is now almost ee 
ally taken for granted. call 
The aa facts in regard to the Eastern American M 
Asiatic floras which these speculations were to explain, ae 
increased in number, more especially through the sa < and 
lections of Dr. Maximowitz in Japan and adjacent ooantti ; 
the critical comparisons he has made and is still engaged bi 
