Affinities: Arctic America. £ 311 
and waters were altered. These seven types are: the circumpolar arctic 
flora, the north temperate continental forest flora, the Pacific 
forest vegetation, the grass land vegetation, the Mexican highland 
flora, the South American and Antillean continental tropic floras. 
It was by the combination and recombination of these several types of vege- 
tation, the sorting and geographic re-arrangement of species in geologic periods 
subsequent to the Cretaceous period, especially during the glacial period, that 
the distribution of the plants of the present North American flora is directly 
traceable. 
Chapter IV. Affinities of North American Flora. 
1. Arctic America. 
In considering the affınities of the flora of arctic North America, it is neces- 
sary to present a few facts and statistics about the arctic flora of the world 
in general. The arctic flora occupies a circumpolar area north of the arctic 
. eircle. There is no abrupt break in the vegetation anywhere along this belt, 
except at Baffın Bay, where a sudden change from an almost purely European 
flora in Greenland on its east coast, to one with a large admixture of American 
plants on its west. Regarded as a whole, the arctic flora is decidediy Scan- 
dinavian, for arctic Scandinavia, or Lapland, though a very small tract of land, 
contains by far the richest arctic flora, amounting to three fourths of the whole; 
more over, according to HOOKER, upwards of three-fifths of the species, and 
almost all of the genera of arctic Asia and America are likewise Lapponian, 
leaving far too small a percentage of other forms to admit ofthe arctic Asiatic 
and American floras being ranked as anything more than subdivisions of one 
general arctic flora. The American district, omitting Greenland, is separable 
into two districts, the eastern American and the western American, 
separated from each other by the estuary of the Mackenzie River. 
The North-American districts. Arctic western America extends from 
Cape Prince of Wales on the east shore of Bering Strait to the estuary of the 
Mackenzie River, and as a whole, it differs from the flora of the district to 
the east by the far greater number of both of European and Asiatic species 
by containing various Altaic and Siberian plants, which do not reach so high 
a latitude in more western meridians and by some temperate plants pecular 
to western America. The number of phanerogamic plants found in arctie 
western America is approximately 364 species. Of these 364 species almost 
all but the littoral and purely arctic species are found in west temperate North 
America, or in the Rocky Mountains, 26 in the Andes of the tropic, or sub- 
tropic America and 37 in temperate or antarctic South America. Comparing * 
this flora with that of temperate and arctic Asia, no less than 320 species are 
found on the north-western shores and islands of that continent, or in Siberia, 
many extending to the Altai and Himalaya Mountains. A comparison with 
