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
{142} 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, {143} use, and disuse,
have, in some cases, played a considerable part in the modification of the
constitution, and of the structure of various