23 to 4.25 that some of the illegitimate unions
yielded during neither year a single seed; but, judging from the long-styled
plants, it is probable, if such unions were to be effected repeatedly by the aid
of insects under the most favourable conditions, some few seeds would be
produced in every case. Anyhow, it is certain that in all twelve illegitimate
unions the pollen-tubes penetrated the stigma in the course of eighteen hours.
At first I thought that two kinds of pollen placed together on the same stigma
would perhaps yield more seed than one kind by itself; but we have seen that
this is not so with each form's own two kinds of pollen; nor is it probable in
any case, as I occasionally got, by the use of a single kind of pollen, fully as
many seeds as a capsule naturally fertilised ever produces. Moreover the pollen
from a single anther is far more than sufficient to fertilise fully a stigma;
hence, in this as with so many other plants, more than twelve times as much of
each kind of pollen is produced as is necessary to ensure the full fertilisation
of each form. From the dusted condition of the bodies of the bees which I caught
on the flowers, it is probable that pollen of various kinds is often deposited
on all three stigmas; but from the facts already given with respect to the two
forms of Primula, there can hardly be a doubt that pollen from the stamens of
corresponding length placed on a stigma would be prepotent over any other kind
of pollen and obliterate its effects,--even if the latter had been placed on the
stigma some hours previously.
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