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.
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