For selection
removes the effect of spontaneous crosses from the variety in each year,
and renders it practically pure, while it is wholly inadequate to
produce the same effects on the species, because of the concealed
hybrids.
The explanation given in this simple instance may be applied to the case
of different varieties of the same species, when growing together and
crossed naturally by insects.
It would take too long to go into all the details that present
themselves here to the student of nature and of gardens. I will only
state, that since varieties differ principally from their species by the
lack of some sharp character, one variety may be characterized by the
lack of color of the flowers, another by the lack of pubescence, a third
by being dwarfed, and so on. Every character must be studied separately
in its effects on the offspring [213] of the crosses. And it is
therefore easily seen, that the hybrids of two varieties may resemble
neither of them, but revert to the species itself. This is necessarily
and commonly the case, since it is always the older or positive
characters that prevail in the hybrids and the younger or negative that
lie hidden. So for instance, a blue dwarf larkspur, crossed with a tall
white variety, must give a tall blue hybrid, reassuming in both
characters the essentials of the species.
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