It is notorious that each species is adapted
to the climate of its own home: species from an arctic or even from a
temperate region cannot endure a tropical climate, or conversely. So
again, many succulent plants cannot endure a damp climate. But the
degree of adaptation of species to the climates under which they live
is often overrated. We may infer this from our frequent inability to
predict whether or not an imported plant will endure our climate, and
from the number of plants and animals brought from warmer countries
which here enjoy good health. We have reason to believe that species
in a state of nature are limited in their ranges by the competition of
other organic beings quite as much as, or more than, by adaptation to
particular climates. But whether or not the adaptation be generally
very close, we have evidence, in the case of some few plants, of their
becoming, to a certain extent, naturally habituated to different
temperatures, or becoming acclimatised: thus the pines and
rhododendrons, raised from seed collected by Dr. Hooker from trees
growing at different heights on the Himalaya, were found in this
country to possess different constitutional powers of resisting cold.
Mr. Thwaites informs me that he has observed similar facts in Ceylon,
and analogous observations have been made by Mr. H. C. Watson on
European species of plants brought from the Azores to England. In
regard to animals, several authentic cases could be given of species
within historical times having largely extended their range from
warmer to cooler latitudes, and conversely; but we do not positively
know that these animals were strictly adapted to their native climate,
but in all ordinary cases we assume such to be the case; nor do we
know that they have subsequently become acclimatised to their new
homes.
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