Primula auricula : 119.

Primula Sikkimensis : 57.

Primula cortusoides : 93.

Primula involucrata : 74.

Primula farinosa : 63.

We thus see that, with the exception of P. auricula, the long-styled flowers of
all nine species are more fertile than the short-styled flowers, when both forms
are illegitimately fertilised. Whether P. auricula really differs from the other
species in this respect I can form no opinion, as the result may have been
accidental. The degree of self-fertility of a plant depends on two elements,
namely, on the stigma receiving its own pollen and on its more or less efficient
action when placed there. Now as the anthers of the short-styled flowers of
several species of Primula stand directly above the stigma, their pollen is more
likely to fall on it, or to be carried down to it by insects, than in the case
of the long-styled form. It appears probable, therefore, at first sight, that
the lessened capacity of the short-styled flowers to be fertilised with their
own pollen, is a special adaptation for counteracting their greater liability to
receive their own pollen, and thus for checking self-fertilisation. But from
facts with respect to other species hereafter to be given, this view can hardly
be admitted. In accordance with the above liability, when some of the species of
Primula were allowed to fertilise themselves spontaneously under a net, all
insects being excluded, except such minute ones as Thrips, the short-styled
flowers, notwithstanding their greater innate self-sterility, yielded more seed
than did the long-styled. None of the species, however, when insects were
excluded, made a near approach to full fertility. But the long-styled form of P.