in the origin of our breeds. When several breeds have
once been formed in any country, their occasional intercrossing, with
the aid of selection, has, no doubt, largely aided in the formation
of new sub-breeds; but the importance of crossing has been much
exaggerated, both in regard to animals and to those plants which are
propagated by seed. With plants which are temporarily propagated by
cuttings, buds, etc., the importance of crossing is immense; for the
cultivator may here disregard the extreme variability both of hybrids
and of mongrels, and the sterility of hybrids; but plants not propagated
by seed are of little importance to us, for their endurance is only
temporary. Over all these causes of change, the accumulative action of
selection, whether applied methodically and quickly, or unconsciously
and slowly, but more efficiently, seems to have been the predominant
power.

CHAPTER II. VARIATION UNDER NATURE.

Variability--Individual differences--Doubtful species--Wide ranging,
much diffused, and common species, vary most--Species of the larger
genera in each country vary more frequently than the species of the
smaller genera--Many of the species of the larger genera resemble
varieties in being very closely, but unequally, related to each other,
and in having restricted ranges.

Before applying the principles arrived at in the last chapter to organic
beings in a state of nature, we must briefly discuss whether these
latter are subject to any variation. To treat this subject properly, a
long catalogue of dry facts ought to be given; but these I shall reserve
for a future work. Nor shall I here discuss the various definitions
which have been given of the term species. No one definition has
satisfied all naturalists; yet every naturalist knows vaguely what
he means when he speaks of a species. Generally the term includes the
unknown element of a distinct act of creation. The term "variety" is
almost equally difficult to define; but here community of descent is
almost universally implied, though it can rarely be proved. We have also
what are called monstrosities; but they graduate into varieties. By a
monstrosity I presume is meant some considerable deviation of structure,
generally injurious, or not useful to the species. Some authors use
the term "variation" in a technical sense, as implying a modification
directly due to the physical conditions of life; and "variations" in
this sense are supposed not