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
The average height of the six crossed plants is here 86 inches, whilst
that of the six self-fertilised plants is only 65.66 inches, so that the
crossed plants are to the self-fertilised in height as 100 to 76. It
should be observed that this difference is not due to a few of the
crossed plants being extremely tall, or to a few of the self-fertilised
being extremely short, but to all the crossed plants attaining a greater
height than their antagonists. The three pairs in Pot 1 were measured at
two earlier periods, and the difference was sometimes greater and
sometimes less than that at the final measuring. But it is an
interesting fact, of which I have seen several other instances, that one
of the self-fertilised plants, when nearly a foot in height, was half an
inch taller than the crossed plant; and again, when two feet high, it
was 1 3/8 of an inch taller, but during the ten subsequent days the
crossed plant began to gain on its antagonist, and ever afterward
asserted its supremacy, until it exceeded its self-fertilised opponent
by 16 inches.
The five crossed plants in Pots 1 and 2 were covered with a net, and
produced 121 capsules; the five self-fertilised plants produced
eighty-four capsules, so that the numbers of capsules were as 100 to 69.
Of the 121 capsules on the crossed plants sixty-five were the product of
flowers crossed with pollen from a distinct plant, and these contained
on an average 5.23 seeds per capsule; the remaining fifty-six capsules
were spontaneously self-fertilised. Of the eighty-four capsules on the
self-fertilised plants, all the product of renewed self-fertilisation,
fifty-five (which were alone examined) contained on an average 4.85
seeds per capsule. Therefore the cross-fertilised capsules, compared
with the self-fertilised capsules, yielded seeds in the proportion of
100 to 93. The crossed seeds were relatively heavier than the
self-fertilised seeds. Combining the above data (i.e., number of
capsules and average number of contained seeds), the crossed plants,
compared with the self-fertilised, yielded seeds in the ratio of 100 to
64.
These crossed plants produced, as already stated, fifty-six
spontaneously self-fertilised capsules, and the self-fertilised plants
produced twenty-nine such capsules. The former contained on an average,
in comparison with the latter, seeds in the proportion of 100 to 99.
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