JVo.l.] GRAY AND HOOKER ON THE KOCKY MOCNTAIN FLOKA. 71 



To complete the view, let it be noted thai the division of these forests Into conifer- 

 ous and non-coniferous is. for the — 



Genera. Speciea. 



European non-coniferous 



European coniferous \ 17 



Japan-Mauohurian non-coniferous i" 123 



Japan-Manohuriaii coniferous 19 \-> 



86 l»w 



In otlici words, a narrow region in Eastern Ajsia contains twice as many genera and 

 about twice as many species of indigenous trees as arc possessed by all Europe; and 

 ■a fco coniferous trees, the former has mor< genera than the latter has species, and 

 over twice and a half as many species 



The only question about the relation of these four forest region-, as to their oom- 

 poneut species, which we can here pause to answer, is to what extent they contain 

 trees of identical species. If we took the shrubs, there would be a small number, if 

 the herbs, a very considerable number, of species common to the two New World and 

 to the two Old World areas, respectively, at least to their northern portions, even after. 

 excluding arctic-alpine plants. The same may be said, in its degree, of the North 

 European flora compared with the Atlantic North American, of the Northeast Asiatic 

 compared with the northern part of the Pacific North American, and also in a peculiar 

 way (which 1 have formerly pointed out. and shall have soon to mention) of the North- 

 eastern Asiatic flora in its relations to the Atlantic North American. But as to the fort si 

 here is very little community of species. Yet this is not absolutely wanting. 

 The Red Cedar (Juniperiu Virf/iniana) among coniferous trees, and Popuhis tremulouks 

 among the deciduous, extend across the Americau continent specifically unchanged, 

 though hardly developed as forest trees on the Pacific side. There are probably, but 

 not Certainly, one or two instances on the northern verge of these two forests. There 

 art as many in which eastern and western species are suggestively similar. The Hem- 

 lock-Spruce of the Northern Atlantic States and the Yew of Florida are extremely like 

 corresponding trees of the Pacific forest. Indeed, the Yew-trees of all four regions 

 may come to be regarded as forms of one polymorphous species. The White Birch of 

 Europe and that of Canada and New England are in similar case, and BO is the com- 

 mon Chestnut (in America confined to the Atlantic States), which, on the other side. 

 of the world, is also represented in Japan. A link in the other direction is seen in 

 one Spruce-tree (called in Oregon Menziee Spruce) which inhabits Northeast Asia, 

 while a peculiar form of it represents the Bpecies of the Rocky Mountains. 



Bat now other and more theoretical questions conic to be asked, Bucfa as these ■ 



Why should our Pacific forest region, which is rich and in some respects unique in 

 coniferous, be so poor in deciduous 



Then the two Big-trees, Sequoias, as Isolated in character as In Location — being 

 found only in ( 'alifornia, and having no neai relatives anywhere — how came California 

 to have them .' 



Such relatives ;i ^ the Sequoias have are also local, peculiar, and chiefly of one 

 - to each genus. Only one of them is American, and that solelj eastern, the 



Taxodium of our Atlantic State- and the plateau of Mexico. The Others M 

 and ( hi:.' 



Why should trees of sis related genera, w hich w ill all thrive in Europe, be rest i 

 naturalh . one to th side of the Am< rican continent, one genus t. . t h. u . 



od very locally, the rest to s small portion of the eastern bordei 



Why should eonifei 



in tl ;ld ? 



