Or, again, the wolves inhabiting a mountainous district, and those
frequenting the lowlands, would naturally be forced to hunt different
prey; and from the continued preservation of the individuals best
fitted for the two sites, two varieties might slowly be formed. These
varieties would cross and blend where they met; but to this subject of
intercrossing we shall soon have to return. I may add, that, according
to Mr. Pierce, there are two varieties of the wolf inhabiting the
Catskill Mountains in the United States, one with a light
greyhound-like form, which pursues deer, and the other more bulky,
with shorter legs, which more frequently attacks the shepherd's
flocks.
Let us now take a more complex case. Certain plants excrete a sweet
juice, apparently for the sake of eliminating something injurious from
their sap: this is effected by glands at the base of the stipules in
some Leguminosae, and at the back of the leaf of the common laurel.
This juice, though small in quantity, is greedily sought by insects.
Let us now suppose a little sweet juice or nectar to be excreted by
the inner bases of the petals of a flower. In this case insects in
seeking the nectar would get dusted with pollen, and would certainly
often transport the pollen from one flower to the stigma of another
flower. The flowers of two distinct individuals of the same species
would thus get crossed; and the act of crossing, we have good reason
to believe (as will hereafter be more fully alluded to), would produce
very vigorous seedlings, which consequently would have the best chance
of flourishing and surviving.
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