lands of Spain; or that the effects of an unvarying temperature,
as at Quito, in the table-land of Peru, are to cause the culture of
wheat to cease at the mean temperature of Milan, and woods to
disappear at the mean of Penzance. A few remarks respecting our own
country is all that we can now find room for.

Including snow-falls, the number of rainy days in Dublin in a year is
208, in London, 178, while in Copenhagen it is not more than 134. The
number of British plants indigenous or naturalised is from 1400 to
1500, comprising mostly the vegetation of Central Europe, but
including specimens from Scandinavia and the Pyrenees. The highest
point at which grain has been known to grow, is 1600 feet above the
sea-level, at the outlet of Loch Collater, in the Highlands. In
Drumochter Pass, an elevation of 1530 feet, potatoes can scarcely be
raised; and from 1000 to 1200 feet is the more common limit of the
cereal and the esculent. On this point a statement is made, which may
be useful to cultivators in the hill districts: it is, that 'the
common brake-fern (_Pteris aquilina_), distributed throughout Britain,
is found to be limited by a line running nearly level with the limit
of cultivation, and thus affords a test, when cultivation may be
absent, where nature does not deny it success. In one sheltered spot
in the woods of Loch-na-gar, it was observed at 1900 feet; and in
another part of the same woods, at 1700 feet; but on the exposed moors
it is very seldom seen beyond 1200 feet, unless in hollows, or on
declivities facing the sun.'

In accounting for the varieties of plants in Britain, it is assumed
that, during the glacial period, when the tops of our mountains were
mere islands in a great sea, under which lay the greater part of
modern Europe, they were then peopled by the arctic and alpine
species, which now inhabit them. Then came an upheaval; a vast tract
of land rose above the water, without any break, as at present between
England and the continent; and at this period 'there appears to have
been a migration of both plants and animals from east to west, the
descendants of which still constitute the great body of the flora and
fauna of the British lowlands.' Meantime, the elevation of the former
islands into mountain summits, placed them in a temperature suited to
the perpetuation of their vegetation. Then, to account for the
presence of a Spanish flora in the west of Ireland, a bold hypothesis,
started by Professor