~ Botanical Geography. @ CC AA, 
portions, but increases gradually towards the north. The 
temperature diminishes very rapidly as we advance north- 
wards, the cold waters of the Polar sea having no sufficient 
outflow southwards through the narrow Behring’s Strait and 
Hudson’s Bay. Europe has also the advantage of a less 
variable maritime climate, from the inland seas penetrating | 
to a greater depth. In consequence of this, New York has 
the summer-temperature of Rome and the winter temperature 
of Copenhagen ; Quebec the summer of Paris and the winter 
of Petersburg. The character of the vegetation is determined 
by this alternation of summer and winter temperatures. 
The northern belt includes the zone of Pinus alba 
and gra, which in America replace the European firs. 
Coniferous forests, the individuals of which are often of an 
immense size, mixed with a few exogenous trees, mark, in 
the zone of the Oregon pine, the passage to that of de- 
ciduous exogenous trees. These forests are distinguished 
from the corresponding oak- and beech-zones of Europe by — 
the greater variety of their oaks, and by the species of elm, 
ash, and maple. ‘The forest-zone of the Southern States . 
is, as in South Europe, characterised by evergreen ex- 
ogenous trees intermixed with representatives of tropical 
families. In its moist summer the climate of these States 
resembles that of China; the most noticeable crops are 
cotton, rice, and the sugar-cane. But these advantages are 
again partially counterbalanced by the sandy and marshy 
nature of the soil from Louisiana to Virginia, [the Great 
Dismal Swamp], covered by Pinus australis, and by the 
almost inaccessible swampy lowlands of the Atlantic 
coast. 
Most European crops thrive in North America as well as 
with us; but the great alternations of temperature are un- 
favourable to the more tropical species, as the orange. The — 
maize is cultivated to higher latitudes than in Europe, while ~ 
- the cultivation of the grape-vine is scarcely anywhere carried 
on with much success. ° 
