1879. ] Distribution of the North American Flora. 159 
ble into three; the first extends from Behring’s straits to the 
mouth of the McKenzie river, and is marked by the presence of 
certain Asiatic genera and species that advance no farther east- 
ward ; the second extends thence onwards to Baffin’s bay, and 
presents various American genera and species not found either 
eastward or westward of it; and the third is that of Greenland, 
which is almost exclusively European, and presents several 
anomalies which I shall hereafter discuss. Besides this eastern 
and western distribution of the Arctic flora, it streams southward 
along the three meridional mountain chains of the continent. 
British North American Flora.—South of the Arctic flora is 
that of the British possessions, that is, of temperate America 
north of the 47th parallel; it consists of a mixture of North 
European, North Asiatic and American genera, in very different 
proportions, disposed in five meridional belts. 1, to the eastward, 
the Canadian forest region; 2, the woodless region, a continua- 
tion of the prairie region farther south; 3, the Rocky mountain 
region, where Mexican genera appear; 4, a dry region, a contin- 
uation of the Desert or Sink regions to the south of it; and 5, 
the Pacific region, which assimilates very closely in its vegetation - 
to that of Kamtschatka. 
United States Flora.—It is on entering the United States that 
the flora of temperate North America attains its great develop- 
ment of genera and species in all the meridians, and that the 
boundaries of the meridional belts of vegetation are most strictly 
defined. 
I. The great eastern forest region, extending over half the 
continent, and consisting of mixed deciduous and evergreen 
trees, reaches from the Atlantic to beyond the Mississippi, dwind- 
ling away as it ascends the western feeders of that river on the 
prairie. It is noteworthy for the number of kinds especially of 
deciduous trees and shrubs that are to be found in it, even ona 
very limited area. Of this I shall select two examples from my > 
journal. One was a patch of native forest a few miles from St. 
Louis, on the Missouri, where in a little more than half an hour, 
and less than a mile’s walk, I saw forty kinds of timber trees,’ 
including eleven of oak, two of maple, two of elm, three of ash, 7s 
two of walnut, six of hickory, three of willow and one each of 
1For the indication and names of them I am indebted to Di Se of St. 
Louis, who took me to the forest. — 
