162 Distribution of the North American Flora. [ March, 
identical with trees of the eastern forests, though several are rep- 
resentative of them. New Mexican genera occur at all elevations 
from the crest of the range to its base, and thence extend across 
the Californian valley and the coast-ranges to the Pacific, mixed 
with northern West American genera and species. 
In this slight outline of the botanical features of temperate and 
Arctic North America, I have alluded to three as most note- 
worthy, namely: the vegetation of Greenland, the Asiatic char- ` 
acter of the vegetation of the eastern half of the continent, and 
the more southern and even Mexican character of the vegetation 
of the western half. How are these features to be accounted for ? 
It so happened that Dr. Gray, Prof. of Botany in Harvard Col- 
lege (Cambridge), and I were contemporaneously, but without con- 
cert, engaged in botanical investigations which have resulted in 
explanations of the two first features. He was at work on the 
flora of Japan,} I on that of the Polar zone, and we were both 
bringing to bear upon our subjects considerations regarding the 
variation of species which Mr. Darwin? almost simultaneously 
laid before the public, and which, I need not say, powerfully 
directed our studies. 
The Greenland Flora—TI shall take the vegetation of Greenland 
first, as being first in order, though second in date of appearance 
and least in importance. Its chief peculiarities are: 1, that its 
plants are almost all of them Scandinavian (that is, North-west ` 
European), hardly any of the peculiar plants of the American 
arctic sea-coast and polar islands crossing Baffin’s bay and Davis 
straits; 2, that of its three hundred flowering plants hardly any 
present even a variation from their Scandinavian prototypes ; 3, 
that it is poorer in species than is any other division of the arctic 
flora, and wants many Scandinavian plants that are found in most 
other arctic countries; 4, that though Greenland extends four 
hundred miles south of the Arctic circle, its extra-arctic continu- 
ation adds only about one hundred species to the flora, and these 
1 « Observations upon the Relations of the Japanese Flora to that of North Amer- 
ica, and of other parts of the North Temperate Zone.” Memoirs of the American 
Academy of Sciences, Vol. vi, p. 377- Read December 14, 1858, and January 11, 
: x Outlines of the Distribution of Arctic Plants.” Read before the Linnæan Soci- 
ety of London, June 21, 1860. Trans. Linn. Soc., XXIII, p. 257. 
3 « On the Tendency a Species to form Varieties,’’ by C. Darwin, Esq., F.R.S., and 
Alf. Wallace, Es]. Read July 1, 1858. Journal of the pene of the Linnaan 
Soc ety of London, Vol. 111 a p. 45- 
