ed to their progeny. As before shown, it is certain that they
sometimes are, which is sufficient reason to avoid such for breeding
purposes. It is also well known that, in the horse, for instance,
certain forms of limbs predispose to certain diseases, as bone spavin
is most commonly seen where there is a disproportion in the size of
the limb above and below the hock, and others might be named of
similar character; in all such cases the disease may be caused by an
agency which would be wholly inadequate in one of more perfect form,
but once existing, it is liable to be reproduced in the offspring--all
tending to show the great importance of _giving due heed_ in selecting
breeding animals _to all qualities, both external and internal_, so
long as "like produces like."

FOOTNOTES:

[2] Finlay Dun, V.S., in Journal of the Royal Agricultural Society.

CHAPTER III.

THE LAW OF VARIATION.

We come now to consider another law, by which that of similarity is
greatly modified, to wit, the law of variation or divergence. All
organic beings, whether plants or animals, possess a certain
flexibility or pliancy of organization, rendering them capable of
change to a greater or less extent. When in a state of nature
variations are comparatively slow and infrequent, but when in a state
of domestication they occur much oftener and to a much greater extent.
The greater variability in the latter case is doubtless owing, in some
measure, to our domestic productions being reared under conditions of
life not so uniform, and different from, those to which the parent
species was exposed in a state of nature.

Flexibility of organization in connexion with climate, is seen in a
remarkable degree in Indian corn. The small Canada variety, growing
only three feet high and ripening in seventy to ninety days when
carried southward, gradually enlarges in the whole plant until it may
be grown twelve feet high and upwards, and requires one hundred and
fifty days to ripen its seed. A southern variety brought northward,
gradually dwindles in size and ripens earlier until it reaches a type
specially fitted to its latitude.

Variation, although the same in kind, is greater in degree, among
domesticated plants than among animals. From the single wild variety
of the potato as first discovered and taken to Europe, have sprung
innumerable sorts. Kemp, in his work on Agricultural Physiology, tells
us, that on the maritime cliffs of England, there