multitude of flowers have their anthers and stigmas fully exposed to
the weather! but if an occasional cross be indispensable, the fullest
freedom for the entrance of pollen from another individual will explain
this state of exposure, more especially as the plant s own anthers and
pistil generally stand so close together that self-fertilisation seems
almost inevitable. Many flowers, on the other hand, have their organs
of fructification closely enclosed, as in the great papilionaceous or
pea-family; but in several, perhaps in all, such flowers, there is a
very curious adaptation between the structure of the flower and the
manner in which bees suck the nectar; for, in doing this, they either
push the flower s own pollen on the stigma, or bring pollen from
another flower. So necessary are the visits of bees to papilionaceous
flowers, that I have found, by experiments published elsewhere, that
their fertility is greatly diminished if these visits be prevented.
Now, it is scarcely possible that bees should fly from flower to
flower, and not carry pollen from one to the other, to the great good,
as I believe, of the plant. Bees will act like a camel-hair pencil, and
it is quite sufficient just to touch the anthers of one flower and then
the stigma of another with the same brush to ensure fertilisation; but
it must not be
supposed that bees would thus produce a multitude of hybrids between
distinct species; for if you bring on the same brush a plant s own
pollen and pollen from another species, the former will have such a
prepotent effect, that it will invariably and completely destroy, as
has been shown by Gartner, any influence from the foreign pollen.
When the stamens of a flower suddenly spring towards the pistil, or
slowly move one after the other towards it, the contrivance seems
adapted solely to ensure self-fertilisation; and no doubt it is useful
for this end: but, the agency of insects is often required to cause the
stamens to spring forward, as Kolreuter has shown to be the case with
the barberry; and curiously in this very genus, which seems to have a
special contrivance for self-fertilisation, it is well known that if
very closely-allied forms or varieties are planted near each other, it
is hardly possible to raise pure seedlings, so largely do they
naturally cross. In many other cases, far from there being any aids for
self-fertilisation, there are special contrivances, as I could show
from the writings of C. C. Sprengel and from my own observations, which
effectually prevent the stigma receiving pollen from its own flower:
for instance, in Lobelia fulgens, there is a really beautiful and
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