“It may be worth while to give another and more complex illustration of
the action of natural selection. Certain plants excrete sweet juice,
apparently for the sake of eliminating something injurious from the sap:
this is effected, for instance, by glands at the base of the stipules in
some Leguminosæ, and at the backs of the leaves of the common laurel.
This juice, though small in quantity, is greedily sought by insects; but
their visits do not in any way benefit the plant. Now, let us suppose
that the juice or nectar was excreted from the inside of the flowers of
a certain number of plants of any species. Insects in seeking the nectar
would get dusted with pollen, and would often transport it from one
flower to another. The flowers of two distinct individuals of the same
species would thus get crossed; the act of crossing, as can be fully
proved, gives rise to vigorous seedlings, which consequently would have
the best chance of flourishing and surviving. The plants which produced
flowers with the largest glands or nectaries, excreting most nectar,
would oftenest be visited by insects, and would oftenest be crossed; and
so in the long run would gain the upper hand and form a local variety.”
The reader will notice that the sweet juice or nectar secreted by
certain plants is supposed to have first appeared independently of the
action of natural selection. Why then account for its presence in
flowers as the outcome of an entirely different process? If the nectar
is eagerly sought for by insects, without the plant benefiting in any
way by their visitations, why give a different explanation of its origin
in flowers where it is of benefit to the plant?
Public-domain text, read in full here on John Shaqi.
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