bility of
constitution, brought, under peculiar circumstances, into play.

How much of the acclimatisation of species to any peculiar climate is
due to mere habit, and how much to the natural selection of varieties
having different innate constitutions, and how much to both means
combined, is a very obscure question. That habit or custom has some
influence I must believe, both from analogy, and from the incessant
advice given in agricultural works, even in the ancient Encyclopaedias
of China, to be very cautious in transposing animals from one district
to another; for it is not likely that man should have succeeded in
selecting so many breeds and sub-breeds with constitutions specially
fitted for their own districts: the result must, I think, be due to
habit. On the other hand, I can see no reason to doubt that natural
selection will continually tend to preserve those individuals which
are born with constitutions best adapted to their native countries. In
treatises on many kinds of cultivated plants, certain varieties are
said to withstand certain climates better than others: this is very
strikingly shown in works on fruit trees published in the United States,
in which certain varieties are habitually recommended for the northern,
and others for the southern States; and as most of these varieties are
of recent origin, they cannot owe their constitutional differences to
habit. The case of the Jerusalem artichoke, which is never propagated
by seed, and of which consequently new varieties have not been produced,
has even been advanced--for it is now as tender as ever it was--as
proving that acclimatisation cannot be effected! The case, also, of the
kidney-bean has been often cited for a similar purpose, and with
much greater weight; but until some one will sow, during a score of
generations, his kidney-beans so early that a very large proportion are
destroyed by frost, and then collect seed from the few survivors, with
care to prevent accidental crosses, and then again get seed from these
seedlings, with the same precautions, the experiment cannot be said to
have been even tried. Nor let it be supposed that no differences in the
constitution of seedling kidney-beans ever appear, for an account has
been published how much more hardy some seedlings appeared to be than
others.

On the whole, I think we may conclude that habit, use, and disuse, have,
in some cases, played a considerable part in the modification of the
consti