THE FLORA OF JAPAN. 133 
nearly peculiar to two regions furnishes evidence of similar 
nature and of equal pertinency with representation by identi- 
cal species, will hardly be doubted. Whether or not suscep- 
tible of scientific explanation, it is certain that related species 
of phzenogamous plants are commonly associated in the same 
region, or are found in comparatively approximate (however 
large) areas of similar climate.1 Remarkable exceptions may 
indeed be adduced, but the fact that they are remarkable goes 
to confirm the proposition. Indeed, the general expectation 
of botanists in this regard sufficiently indicates the common, 
implicit opinion. The discovery of a new Sarracenia or of 
a new Halesia in the Atlantic United States, or of a new 
Eschscholtzia, Platystemon, or Calais west of the Rocky 
Mountains, would excite no surprise. A converse discovery, 
or the detection of any of these genera in a remote region, 
would excite great surprise. The discovery of numerous 
closely related species thus divided between two widely sepa- 
rated districts might not, in the present state of our knowl- 
edge, suggest former continuity, migration, or interchange ; 
1 The fundamental and most difficult question remaining in natural 
history is here presented —the question whether this actual geographi- 
eal 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 the “Journal of the Proceedings of the 
Linnean Society,” vol. iii. (Zodlogy), 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 ten- 
dencies and causes indicated are really operative ; the question is as to the 
extent of their operation. But I am already disposed, on these and other 
grounds, to admit that what are termed closely related species may in 
many cases be lineal descendants from a pristine stock, just as domesti- 
cated 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 gener- 
ally supposed, and that derivative forms when segregated may be as con- 
stantly reproduced as their originals. 
