310 THE ORIGIN OF THE FLORA OF ATLANTIC NORTH AMERICA. 
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 elimate grew warmer; that the general difference of climate which 
marks the eastern and western sides of the continents—the one extreme, 
the other mean—was doubtless 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 regious of different distribution of heat an 
moisture ; so that different species of the same genus, as iu Torreya, or 
different genera of the same group, as Redwood, Taxodium, and Glypto- 
strobus, or different associations of forest-trees, might establish themselves 
in the region best suited to their 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 in, and pre-supposed, an ancestry in pliocene or still earlier 
times occupying the high northern regions. 
“ And it was thought that the occurrence of peculiarly North American 
genera in Europe in the tertiary period (such as Taxodium, Carya, Liqui- 
dambar, Sassafras, Negundo, etc.), might best be explained on the assump- 
tion of early interchange and diffusion through North Asia, rather than 
by that of the fabled Atlantis. 
count for little if the two grew in the same country, 
many of my list of identical to that of representative species; an 
by simply eliminating from consideration the whole array of re resenta- 
ive species, że., all cases in which the Japanese and the American plants 
are not exactly alike, 
“ As if by pronouncing the cabalistic word ‘ species ° the question T 
settled, or, rather, the greater part of it remanded out of the domam ot 
TOONE; a if, while complete identity of forms implied community 
origin, anything short of it carried no presumption of the kind—s¢ 
eaving all these singular duplicates to be wondered at, indeed, but wholl; 
beyond the reach of inquiry ! 
thus transferring 
d then 
