ACCLIMATISATION.
Habit is hereditary with plants, as in the period of flowering, in the time
of sleep, in the amount of rain requisite for seeds to germinate, etc., and
this leads me to say a few words on acclimatisation. As it is extremely
common for distinct species belonging to the same genus to inhabit hot and
cold countries, if it be true that all the species of the same genus are
descended from a single parent-form, acclimatisation must be readily
effected during a long course of descent. 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 different countries which are
here perfectly healthy. We have reason to believe that species in a state
of nature are closely 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 this adaptation is in most cases very close,
we have evidence with some few plants, of their becoming, to a certain
extent, naturally habituated to different temperatures; that is, they
become acclimatised: thus the pines and rhododendrons, raised from seed
collected by Dr.
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