﻿ON THE BOTANY OF JAPAN. 443 



Europe is almost complete, and is most strikingly in contrast with the large number of 

 Eastern American forms repeated or represented in Eastern Asia. Of genera divided 

 between Eastern North America and Europe, I can mention only Ostrya, Narthecium, 

 Psamma, the maritime Cakile, and perhaps Scolopendrium. Hottonia might have been 

 added, but for a species accredited to Java. And if we extend the range across our con- 

 tinent, we add only Cercis and Lcejiingia. Of the ampler genera at all characteristic of 

 the European flora, I can enumerate from the Flora of the Northern United States 

 nothing more important than Helianthemum and Valerianella, two or three species of 

 each, (but those of the former hardly congeners of the European ones,) adding that 

 Hieracia and perhaps Cirsia are somewhat more plentiful in Eastern than in Western 

 America. Let it also be noted, that there are even fewer Western-European types in 

 the Pacific than in the Atlantic United States, notwithstanding the similarity of the 

 climate ! 



That representation by allied species of genera peculiar, or nearly peculiar, to two 

 regions, furnishes evidence of similar nature and of equal pertinency with represen- 

 tation by identical species, will hardly be doubted. Whether or not susceptible of 

 scientific explanation, it is certain that related species of phaenogamous plants are 

 commonly associated in the same region, or are found in comparatively approximate 

 (however large) areas of similar climate.* Remarkable exceptions may indeed be 

 adduced ; but the fact that they are remarkable goes to confirm the proposition. In- 

 deed, the general expectation of botanists in this regard sufficiently indicates the com- 

 mon, implicit opinion. The discovery of a new Sarracenia or a new Halesia in the 



* The fundamental and most difficult question remaining in natural liistory is here presented ; — the question 

 whether this actual geographical association of congeneric or other nearly related species is primordial, and 

 therefore beyond all scientific explanation, or whether even this may be to a certain extent a natural result. 

 The only noteworthy attempt at a scientific solution of the problem, aiming to bring the variety as well as the 

 geographical association of existing species more within the domain of cause and effect, is that of Mr. Darwin 

 and (later) of Mr. "Wallace, — partially sketched in their short papers " On the Tendency of Species to form 

 Varieties, and on the Perpetuation of Varieties and Species by natural Means of Selection," in tlie Journal of 

 the Proceedings of the Linnaean Society, Vol. 3 (Zoology), p. 45. The views there suggested must bear a 

 prominent part in future investigations into the distribution and probable origin of species. It will hardly be 

 doubted that the tendencies and causes indicated are reaUy operative ; the question is as to the extent of their 

 operation. But I am already disposed, on these and on other grounds, to admit that what are termed closely re- 

 lated species may in many cases be lineal descendants from a pristine stock, just as domesticated races are ; 

 or, in other words, that the limits of occasional variation in species (if by them we mean primordial forms) are 

 wider than is generally supposed, and that derivative forms when segregated may be as constantly reproduced 

 as their originals. 



