elaborate contrivance by which every one of the infinitely numerous
pollen-granules are swept out of the conjoined anthers of each flower,
before the stigma of that individual flower is ready to receive them;
and as this flower is never visited, at least in my garden, by insects,
it never sets a seed, though by placing pollen from one flower on the
stigma of another, I raised plenty of seedlings; and whilst another
species of Lobelia growing close by, which is visited by bees, seeds
freely. In very many other cases, though there be no special mechanical
contrivance to prevent the stigma of a flower receiving its own pollen,
yet, as
C. C. Sprengel has shown, and as I can confirm, either the anthers
burst before the stigma is ready for fertilisation, or the stigma is
ready before the pollen of that flower is ready, so that these plants
have in fact separated sexes, and must habitually be crossed. How
strange are these facts! How strange that the pollen and stigmatic
surface of the same flower, though placed so close together, as if for
the very purpose of self-fertilisation, should in so many cases be
mutually useless to each other! How simply are these facts explained on
the view of an occasional cross with a distinct individual being
advantageous or indispensable!
If several varieties of the cabbage, radish, onion, and of some other
plants, be allowed to seed near each other, a large majority, as I have
found, of the seedlings thus raised will turn out mongrels: for
instance, I raised 233 seedling cabbages from some plants of different
varieties growing near each other, and of these only 78 were true to
their kind, and some even of these were not perfectly true. Yet the
pistil of each cabbage-flower is surrounded not only by its own six
stamens, but by those of the many other flowers on the same plant. How,
then, comes it that such a vast number of the seedlings are
mongrelized? I suspect that it must arise from the pollen of a distinct
_variety_ having a prepotent effect over a flower s own pollen; and
that this is part of the general law of good being derived from the
intercrossing of distinct individuals of the same species. When
distinct _species_ are crossed the case is directly the reverse, for a
plant s own pollen is always prepotent over foreign pollen; but to this
subject we shall return in a future chapter.
In the case of a gigantic tree covered with innumerable flowers, it may
be objected that pollen could seldom be carried from tree to tree, and
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