ON THE DERIVATION OF AMERICAN PLANTS. 727 



The larger part of the genera of our own region which I have enu- 

 merated as wanting in California are present in Japan or Mantchooria, 

 along with many other peculiar plants divided between the two. 

 There are plants enough of the one region which have no representa- 

 tives in the other. There are types which appear to have reached the 

 Atlantic States from the South, and there is a larger infusion of sub- 

 tropical Asiatic types into temperate China and Japan ; among these 

 there is no relationship "between the two countries to speak of. There 

 are also, as I have already said, no small number of genera and some 

 species, which, being common all round or partially round the northern 

 temperate zone, have no special significance because of their occurrence 

 in these two antipodal floras, although they have testimony to bear 

 upon the general question of geographical distribution. The point to 

 be remarked is that a very large proportion of the genera and species 

 which are peculiar to North America as compared with Europe, and 

 largely peculiar to Atlantic North America as compared with the Cali- 

 fornia region, are also represented in Japan and Mantchooria, either by 

 identical or by closely-similar forms. The same rule holds on a more 

 northward line, although not so strikingly. If we compare the plants, 

 say of New England and Pennsylvania (latitude 45 47'), with those 

 of Oregon, and then with those of Northeast Asia, we shall find 

 many of our own curiously represented in the latter, while only a small 

 number of them can be traced along the route even so far as the west- 

 ern slope of the Rocky Mountains. And these repositories of Eastern- 

 American types in Japan and neighboring districts are in all degrees 

 if likewise. Sometimes the one is undistinguishable from the other ; 

 sometimes there is a difference of as great but hardly of as tangible 

 character ; sometimes the two would be termed marked varieties if 

 they grew naturally in the same forest, or in the same region ; some- 

 times they are what the botanists call representative species, the one 

 answering closely to the other, but with some differences regarded as 

 specific ; sometimes the two are nearly of the same genus or not quite 

 that, but of a single or very few species in each country, when the 

 point which interests us is that this peculiar limited type should occur 

 in two antipodal places and nowhere else. It would be tedious, and, 

 except to botanists, abstruse, to enumerate instances, yet the w T hole 

 strength of the case depends upon the number of such instances. I 

 propose, therefore, if the Association does me the honor to print this 

 discourse, to append in a note a list of the more remarkable ones. But 

 I would mention two or three cases as specimens. Our Minis toxico- 

 dendron, or poison-ivy, is exactly repeated in Japan, but is found in 

 no other part of the world, although a species like it abounds in Cali- 

 fornia. Our other species of Rhus (R. venenata), commonly called 

 poison-dogwood, is in no way represented in Western America, but 

 has so close an alliance in Japan that the two were taken for the same 

 by Thunberg and Linnams, who called them both R, vernix. Our 



