1879. | Distribution of the North American Flora. 161 
hornbeam, birches, alders, willows, beech, poplars, &c. Of those 
confined to America and East Asia I find in America thirty-three 
genera and fifty-five species, including magnolias, tulip tree, 
negundo, wistaria, Virginia creeper, gleditschia, hydrangea, liquid- 
amber, nyassa, tecoma, catalpa, diospyros, sassafras, benzoin, mul- 
berry, walnut and others which, not being European, are unfamil- 
iar to you. Lastly, of those confined to Europe and America I 
find only one genus, namely, the hop-hornbeam, of which there 
is but a single representative in each country. 
Here, then, is conclusive evidence of the close botanical rela- 
tionship of North-eastern Asia and Eastern North America; a 
relationship of which there is but little evidence in the vegetation 
of the prairies and Rocky mountains, and still less, perhaps, in the 
regions farther west. 
lII. The prairie region succeeds a grassy land with many pecu- 
liar herbaceous American- genera, including Mexican types, of 
which last the most conspicuous are a yucca and cacti, which lat- 
ter increase in number as the Rocky mountains are approached, 
where they form a noticeable feature in the landscape. 
In the parks and lower valleys of the Rocky mountains, decid- 
uous trees are few and scattered, and the forest is an open one of 
conifers, amongst which a pine, allied to the American nut-pines, 
P. edulis, first appears. Higher on the mountains the coniferous 
forests are dense, and almost the only deciduous tree is an aspen, 
which forms impenetrable brakes on the slopes and in the gullies. 
Above the forest region are the sub-alpine and alpine regions, 
presenting a mixture of European, Asiatic and American types. 
III. Descending to the Sink region the cacti and yucca almost 
disappear, though they increase to a maximum farther south in 
this meridian. Deciduous trees are very few, and confined to the 
gullies of the mountains, and Mexican genera increase in num- 
bers. The hoary sage-bush (Artemisia) covers immense tracts of 
dry soil, and saline plants occupy the more humid districts. 
Another nut-pine of Mexican affinity (P. monophylla) traverses 
the center of this region in a narrow meridional strip, and the 
proportion of endemic plants, herbaceous especially, is very 
large. ` 
IV. The Sierra Nevada is clothed with the most gigantic conif- o 
erous forest to be found on the globe, amongst which a wy kw 
species of deciduous trees are scattered; but none of t! are 
