Column 2: Number of Plants.
Column 3: Number of Umbels produced.
Column 4: Product of Seed.

Short-styled : 6 : 24 : 1.3 grain weight of seed, or about 50 in number.
Long-styled : 18 : 74 : Not one seed.

Judging from the exposed plants which grew all round in the same bed, and had
been treated in the same manner, excepting that they had been exposed to the
visits of insects, the above six short-styled plants ought to have produced 92
grains' weight of seed instead of only 1.3; and the eighteen long-styled plants,
which produced not one seed, ought to have produced above 200 grains' weight.
The production of a few seeds by the short-styled plants was probably due to the
action of Thrips or of some other minute insect. It is scarcely necessary to
give any additional evidence, but I may add that ten pots of Polyanthuses and
cowslips of both forms, protected from insects in my greenhouse, did not set one
pod, though artificially fertilised flowers in other pots produced an abundance.
We thus see that the visits of insects are absolutely necessary for the
fertilisation of Primula veris. If the corolla of the long-styled form had
dropped off, instead of remaining attached in a withered state to the ovarium,
the anthers attached to the lower part of the tube with some pollen still
adhering to them would have been dragged over the stigma, and the flowers would
have been partially self-fertilised, as is the case with Primula Sinensis
through this means. It is a rather curious fact that so trifling a difference as
the falling-off of the withered corolla, should make a very great difference in
the number of seeds produced by a plant if its flowers are not visited by
insects.

The flowers of the cowslip and of the other species of the genus secrete plenty
of nectar; and I have often seen humble bees, especially B. hortorum and