I was therefore careful to
give an amply sufficient supply of pollen, and generally covered the
stigma with it; but I did not take any special pains to place exactly
the same amount on the stigmas of the self-fertilised and crossed
flowers. After having acted in this manner during two seasons, I
remembered that Gartner thought, though without any direct evidence,
that an excess of pollen was perhaps injurious; and it has been proved
by Spallanzani, Quatrefages, and Newport, that with various animals an
excess of the seminal fluid entirely prevents fertilisation. (1/10.
'Transactions of the Philosophical Society' 1853 pages 253-258.) It was
therefore necessary to ascertain whether the fertility of the flowers
was affected by applying a rather small and an extremely large quantity
of pollen to the stigma. Accordingly a very small mass of pollen-grains
was placed on one side of the large stigma in sixty-four flowers of
Ipomoea purpurea, and a great mass of pollen over the whole surface of
the stigma in sixty-four other flowers. In order to vary the experiment,
half the flowers of both lots were on plants produced from
self-fertilised seeds, and the other half on plants from crossed seeds.
The sixty-four flowers with an excess of pollen yielded sixty-one
capsules; and excluding four capsules, each of which contained only a
single poor seed, the remainder contained on an average 5.
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