150 days in the north and 90 days at Astrakhan, the Don for 100
to 110 days, and the Dneiper for 83 to 122 days. On the Dwina ice
prevents navigation for 125 days and even the Vistula at Warsaw
remains frozen for 77 days. The lowest temperatures are experienced
in January, in which month the average is as low as 20 deg. to 5 deg. Fahr.
throughout Russia; in the west only does it rise above 22 deg..

_The flora and fauna of Russia_.--The flora of Russia, which represents
an intermediate link between those of Germany and Siberia, is strikingly
uniform over a very large area. Though not poor at any given place,
it appears so if the space occupied by Russia be taken into account,
only 3,300 species of phanerogams and ferns being known. Four great
regions may be distinguished:--the Arctic, the Forest, the Steppe,
and the Circum-Mediterranean.

The _Arctic Region_ comprises the _tundras_ of the Arctic littoral
beyond the northern limit of forests, which last closely follows
the coast-line with bends towards the north in the river valleys
(70 deg. N. lat. in Finland, on the Arctic Circle about Archangel, 68 deg.
N. on the Urals, 71 deg. on West Siberia). The shortness of summer,
the deficiency of drainage and the thickness of the layer of soil
which is frozen through in winter are the elements which go to
the making of the characteristic features of the _tundras_. Their
flora is far nearer those of northern Siberia and North America
than that of central Europe. Mosses and lichens cover them, as
also the birch, the dwarf willow, and a variety of shrubs; but
where the soil is drier, and humus has been able to accumulate, a
variety of herbaceous flowering plants, some of which are familiar
also in western Europe, make their appearance.

The _Forest Region_ of the Russian botanists occupies the greater
part of the country, from the Arctic _tundras_ to the Steppes, and
it maintains over this immense surface a remarkable uniformity
of character. Viewed as a whole, the flora of the forest region
must be regarded as European-Siberian; and though certain species
disappear towards the east, while new ones make their appearance,
it maintains, on the whole, the same characters throughout from
Poland to Kamchatka. Thus the beech, a characteristic tree of western
Europe, is unable to face the continental climate of Russia, and
does not penetrate beyond Poland and the south-western provinces,
reappearing again in the Crimea. The silver fi