In scientific works it is commonly used
to designate the occurrence of subspecies or varieties, and the same is
the case in the ordinary use of the term when dealing with cultivated
plants. A species may consist of larger or smaller groups of such units,
and they may be absolutely constant, never sporting if hybridization is
precluded, and nevertheless it may be called highly variable. The
opium-poppy affords a good instance. It "varies" in height, in color of
foliage and flowers; the last are often double or laciniated; it may
have white or bluish seeds, the capsules may open themselves or remain
closed and so on. But every single variety is absolutely constant, and
never runs into another, when the flowers are artificially pollinated
and the visits of insects excluded. So it is with many other species.
They are at the same time wholly stable and very variable.
The terms variation and variety are used frequently when speaking of
hybrids. By crossing forms, which are already variable in the sense just
mentioned, it is easy to multiply the number of the types, and even in
crossing pure forms the different characters may be combined in
different ways, the resulting combinations [190] yielding new, and very
often, valuable varieties. But it is manifest that this form of
variation is of quite another nature from the variations of pure races.
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