﻿442 ON THE BOTANY OF JAPAN. 



the most striking representative species), and almost as many more are divided between 

 North America and extra-tropical (chiefly Northern and Eastern) Asia. About 40 of 

 the latter are genera or groups of single, or of two or few closely related species, pecu- 

 liar, or nearly peculiar, to the regions just mentioned. 



This list should be supplemented by those additional North American genera which 

 have one or more closely representative species in the Himalayan region only, such as 

 Podophi/lhrm, Pyridaria, &c. ; and also by the numerous cases in which Eastern- 

 American plants are represented in the Himalayo-Japanese region by strikingly cognate, 

 although not congeneric species ; such as our Macrotys by Pityrosperma ; Schizandra 

 by Kadsura and Sphcerostema ; Neviusia by Kerria and Rhodotypos ; Calycanthiis by 

 Chimonanthus ; Cornus florida by Benthamia ; Prosartes by Disporum ; Ilelonias by 

 Heloniopsis ; and so of others, which have been mentioned in the former part of this 

 memoir, and exhibited in the accompanying tabular view. 



I had long ago, in Silliman's Journal, presented some data illustrative of this re- 

 markable parallelism, and also more recently, in my " Statistics of the Flora of the 

 Northern United States " (Vol. 22, Second Series) ; where I had noticed the facts, — 

 1. that a large percentage of our extra-European types are shared with Eastern 

 Asia ; and 2. that no small part of these are unknown in Western North America. 

 But Mr. Bentham was first to state the natural conclusion from all these data, — 

 though I know not if he has even yet published the remark, — viz. that the inter- 

 change between the temperate floras even of the western part of the Old World and 

 of the New has mainly taken place via Asia. Notwithstanding the few cases which 

 point in the opposite direction (e. g. Eriocaulon septangulare, Spartitia, Suhularia, 

 Betula alba), the general statement will be seen to be well sustained. Also, in the 

 .Journal of the Proceedings of the Linneean Society, 2. p. 34, Mr. Bentham " calls to 

 mind how frequently large American genera (such as Eiqyatorium, Aster, Solidago, 

 Solanum, &c.) are represented in Eastern Asia by a small number of species, which 

 gradually diminish or altogether disappear as we proceed westward toward the Atlantic 

 limits of Europe ; whilst the types peculiar to the extreme west of Europe (excluding 

 of course the Arctic flora) are wholly deficient in America. These are among the con- 

 siderations which suggest an ancient continuity of territory between America and Asia, 

 under a latitude, or at any rate with a climate, more meridional than would be efiiected 

 by a junction through the chains of the Aleutian and the Kurile Islands." 



I shall presently state why connection in a more meridional latitude need not be 

 supposed. 



The deficiency in the temperate American flora of forms at all peculiar to Western 



