As the flowers are
much frequented by Thrips, the self-fertilisation of most of the flowers
under the net may have been due to the action of these minute insects.
Dr. Ogle likewise covered up a large portion of a plant, and "out of a
vast number of blossoms thus protected not a single one produced a pod,
while the unprotected blossoms were for the most part fruitful." Mr.
Belt gives a more curious case; this plant grows well and flowers in
Nicaragua; but as none of the native bees visit the flowers, not a
single pod is ever produced. (5/6. Dr. Ogle 'Popular Science Review'
1870 page 168. Mr. Belt 'The Naturalist in Nicaragua' 1874 page 70. The
latter author gives a case 'Nature' 1875 page 26, of a late crop of
Phaseolus multiflorus near London which "was rendered barren" by the
humble-bees cutting, as they frequently do, holes at the bases of the
flowers instead of entering them in the proper manner.)
From the facts now given we may feel nearly sure that individuals of the
same variety or of different varieties, if growing near each other and
in flower at the same time, would intercross; but I cannot myself
advance any direct evidence of such an occurrence, as only a single
variety is commonly cultivated in England. I have, however, received an
account from the Reverend W.A. Leighton, that plants raised by him from
ordinary seed produced seeds differing in an extraordinary manner in
colour and shape, leading to the belief that their parents must have
been crossed.
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