The Effects of Cross & Self-Fertilisation in the Vegetable KingdomDarwin, Charles
Science
The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom
Darwin, Charles
Fertilization of plants; Plants -- Variation; Pollination
As the Chinese primrose is a heterostyled or dimorphic plant, like the
common cowslip, it might have been expected that the flowers of both
forms when illegitimately fertilised with their own pollen or with that
from flowers on another plant of the same form, would have yielded less
seed than the legitimately crossed flowers; and that the seedlings
raised from illegitimately self-fertilised seeds would have been
somewhat dwarfed and less fertile, in comparison with the seedlings from
legitimately crossed seeds. This holds good in relation to the fertility
of the flowers; but to my surprise there was no difference in growth
between the offspring from a legitimate union between two distinct
plants, and from an illegitimate union whether between the flowers on
the same plant, or between distinct plants of the same form. But I have
shown, in the paper before referred to, that in England this plant is in
an abnormal condition, such as, judging from analogous cases, would tend
to render a cross between two individuals of no benefit to the
offspring. Our plants have been commonly raised from self-fertilised
seeds; and the seedlings have generally been subjected to nearly uniform
conditions in pots in greenhouses. Moreover, many of the plants are now
varying and changing their character, so as to become in a greater or
less degree equal-styled, and in consequence highly self-fertile. From
the analogy of Primula veris there can hardly be a doubt that if a plant
of Primula sinensis could have been procured direct from China, and if
it had been crossed with one of our English varieties, the offspring
would have shown wonderful superiority in height and fertility (though
probably not in the beauty of their flowers) over our ordinary plants.
My first experiment consisted in fertilising many flowers on long-styled
and short-styled plants with their own pollen, and other flowers on the
same plants with pollen taken from distinct plants belonging to the same
form; so that all the unions were illegitimate. There was no uniform and
marked difference in the number of seeds obtained from these two modes
of self-fertilisation, both of which were illegitimate. The two lots of
seeds from both forms were sown thickly on opposite sides of four pots,
and numerous plants thus raised. But there was no difference in their
growth, excepting in one pot, in which the offspring from the
illegitimate union of two long-styled plants exceeded in a decided
manner in height the offspring of flowers on the same plants fertilised
with their own pollen. But in all four pots the plants raised from the
union of distinct plants belonging to the same form, flowered before the
offspring from the self-fertilised flowers.
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