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
Here the relative heights of the three lots are nearly the same (within
three or four per cent) as with the plants in the pots. In weight there
is a much greater difference: the Westerham-crossed exceed the
self-fertilised by much less than they did before; but the
self-fertilised plants in the pots had become slightly withered, as
before stated, and were in consequence unfairly light. The
Westerham-crossed plants are here inferior in weight to the intercrossed
plants in a much higher degree than in the pots; and this appeared due
to their being much less branched, owing to their having germinated in
greater numbers and consequently being much crowded. Their leaves were
of a brighter green than those of the intercrossed and self-fertilised
plants.
RELATIVE FERTILITY OF THE THREE LOTS OF PLANTS.
None of the plants in pots in the greenhouse ever produced a capsule;
and this may be attributed in chief part to the exclusion of moths.
Therefore the fertility of the three lots could be judged of only by
that of the plants growing out of doors, which from being left uncovered
were probably cross-fertilised. The plants in the three rows were
exactly of the same age and had been subjected to closely similar
conditions, so that any difference in their fertility must be attributed
to their different origin; namely, to the one lot being derived from
plants self-fertilised for four generations and then crossed with a
fresh stock; to the second lot being derived from plants of the same old
stock intercrossed for five generations; and to the third lot being
derived from plants self-fertilised for five generations. All the
capsules, some nearly mature and some only half-grown, were gathered,
counted, and weighed from the ten finest plants in each of the three
rows, of which the measurements and weights have already been given. The
intercrossed plants, as we have seen, were taller and considerably
heavier than the plants of the other two lots, and they produced a
greater number of capsules than did even the Westerham-crossed plants;
and this may be attributed to the latter having grown more crowded and
being in consequence less branched. Therefore the average weight of an
equal number of capsules from each lot of plants seems to be the fairest
standard of comparison, as their weights will have been determined
chiefly by the number of the included seeds. As the intercrossed plants
were taller and heavier than the plants of the other two lots, it might
have been expected that they would have produced the finest or heaviest
capsules; but this was very far from being the case.
The ten tallest Westerham-crossed plants produced 111 ripe and unripe
capsules, weighing 121.2 grains. Therefore 100 of such capsules would
have weighed 109.18 grains.
The ten tallest intercrossed plants produced 129 capsules, weighing
76.45 grains. Therefore 100 of these capsules would have weighed 59.26
grains.
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