THE FLORA OF JAP AX. 131 



Astilbe Leptandra Arundinaria 



Mitella Callicarpa Adiantura 



Hydrangea Cedronella Onoclea 



Itea Amsonia 



Here are about ninety extra-European genera or forms, 

 sixty-four of which are absent from western North America 

 out of the tropics (the latter comprising a very huge part of 

 the most striking representative species), and almost as many 

 more are divided between North America and extra-tropical 

 (chiefly northern and eastern) Asia. About forty of the 

 latter genera are groups of single, or of two or few closely 

 related species, peculiar, 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 representa- 

 tive species in the Himalayan region only, such as Podophyl- 

 lum, Pyrularia, etc. ; and also by the numerous cases in 

 which eastern American plants are represented in the Ilima- 

 layo-Japanese region by strikingly cognate, although not con- 

 generic species; such as our Macrotys by Pityrosperma ; 

 Schizandra by Kadsura and Sphaerostema ; Neviusia by 

 Kerria and Rhodotypus ; Calycanthus by Chimonanthus ; 

 Cornus florida by Benthamia ; Prosartes by Disporum ; 

 Helonias 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 remarkable parallelism, and also more re- 

 cently in my " Statistics of the Flora of the Northern United 

 States " (vol. xxii., second series) ; where I had noticed the 

 facts, — (1) that a large percentage of our extra-Euro] >ean 

 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, — namely, that the interchange between the tem- 

 perate floras even of the western part of the Old World and 

 of the New has mainly taken place via Asia. Not withstand- 



