THE FLORA OF JAPAN. 131 
Astilbe Leptandra Arundinaria 
Mitella Callicarpa Adiantum 
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 large 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 Hima- 
layo-Japanese region by strikingly cognate, although not con- 
generic species; such as our Macrotys by Pityrosperma; 
Schizandra by Kadsura and Spherostema; 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-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, — 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. Notwithstand- 
