ytt (p. 19), "endure the strongest summer heat without
injury, while they are often destroyed when not sufficiently covered
during the winter." Similar observations have been made in other
countries. For this reason they have to be generally wintered in frames
in the Botanic Gardens at Kew and Dublin, and are thus exposed to higher
temperatures than at present obtain in the British Islands. This fact
suggests that the Alpine and Arctic plants really did not originate in
countries with cold temperatures. They probably made their first
appearance long before the Glacial period--perhaps in early Tertiary
times--chiefly in the Arctic Regions, which at that time had a mild
climate. They have since become adapted to live in cold countries where
they flourish, provided they receive sufficient moisture in the summer,
and are protected from severe frost in the winter by a covering of snow.

When we carefully examine the present range of Arctic plants in the
British Islands, a curious fact presents itself which no doubt has
frequently been noted by botanists, viz., that some of the most
characteristically Arctic species, and some which are often quoted by
glacialists in support of their theories, flourish at the present moment
in very mild situations. I have already referred to the fact that the
Mountain Avens (_Dryas octopetala_) abounds in the west of Ireland
(County Galway) down to sea-level. Now it is well known that the mean
winter temperature of that part of Ireland resembles that of Southern
Europe, being no less than 12 deg. F. (=7 deg. Cent.) above freezing point. The
plant, of course, is here a native, and not introduced. This instance
shows clearly, that as long as more vigorous competitors are absent, and
as long as it is not exposed to severe frost or undue dryness, this and
allied species do just as well in a mild climate as in their native
Arctic home.

In his interesting essay on the distribution of the Arctic plants in
Europe during the Glacial period, Professor Nathorst adduces the fact
that all the localities but one, in which remains of such plants have
been discovered, lie either within or close to the limits of the maximum
extension of the supposed northern ice-sheet, or within those of the
former Alpine glaciers. Whether we look upon the boulder-clay as a
marine or a terrestrial product, it is quite conceivable that, in many
instances, the remains of the Arctic plants may have been carried by ice
to great