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Darwin, Charles, 1809-1882

"Effects of Cross and Self Fertilisation in the Vegetable Kingdom"

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SUMMARY ON THE LEGUMINOSAE.
Six genera in this family were experimented on, and the results are in
some respects remarkable. The crossed plants of the two species of
Lupinus were conspicuously superior to the self-fertilised plants in
height and fertility; and when grown under very unfavourable conditions,
in vigour. The scarlet-runner (Phaseolus multiflorus) is partially
sterile if the visits of bees are prevented, and there is reason to
believe that varieties growing near one another intercross. The five
crossed plants, however, exceeded in height the five self-fertilised
only by a little. Phaseolus vulgaris is perfectly self-sterile;
nevertheless, varieties growing in the same garden sometimes intercross
largely. The varieties of Lathyrus odoratus, on the other hand, appear
never to intercross in this country; and though the flowers are not
often visited by efficient insects, I cannot account for this fact, more
especially as the varieties are believed to intercross in North Italy.
Plants raised from a cross between two varieties, differing only in the
colour of their flowers, grew much taller and were under unfavourable
conditions more vigorous than the self-fertilised plants; they also
transmitted, when self-fertilised, their superiority to their offspring.
The many varieties of the common Pea (Pisum sativum), though growing in
close proximity, very seldom intercross; and this seems due to the
rarity in this country of the visits of bees sufficiently powerful to
effect cross-fertilisation.


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