lant." ("Cross and Self fertilisation", page 350.) We
are as ignorant of the reason why plants behave differently when
crossed and self-fertilised as we are in regard to the nature of the
differentiation of the sexual cells, which determines whether a union of
the sexual cells will prove favourable or unfavourable.

It is impossible to discuss the different results of
cross-fertilisation; one point must, however, be emphasised, because
Darwin attached considerable importance to it. It is inevitable that
pollen of different kinds must reach the stigma. It was known that
pollen of the same "species" is dominant over the pollen of another
species, that, in other words, it is prepotent. Even if the pollen of
the same species reaches the stigma rather later than that of another
species, the latter does not effect fertilisation.

Darwin showed that the fertilising power of the pollen of another
variety or of another individual is greater than that of the plant's
own pollen. ("Cross and Self fertilisation", page 391.) This has
been demonstrated in the case of Mimulus luteus (for the fixed
white-flowering variety) and Iberis umbellata with pollen of another
variety, and observations on cultivated plants, such as cabbage,
horseradish, etc. gave similar results. It is, however, especially
remarkable that pollen of another individual of the same variety may be
prepotent over the plant's own pollen. This results from the superiority
of plants crossed in this manner over self-fertilised plants. "Scarcely
any result from my experiments has surprised me so much as this of the
prepotency of pollen from a distinct individual over each plant's own
pollen, as proved by the greater constitutional vigour of the crossed
seedlings." (Ibid. page 397.) Similarly, in self-fertile plants the
flowers of which have not been deprived of the male organs, pollen
brought to the stigma by the wind or by insects from another plant
effects fertilisation, even if the plant's own pollen has reached the
stigma somewhat earlier.

Have the results of his experimental investigations modified the point
of view from which Darwin entered on his researches, or not? In the
first place the question is, whether or not the opinion expressed in
the Orchid book that there is "Something injurious" connected with
self-fertilisation, has been confirmed. We can, at all events, affirm
that Darwin adhered in essentials to his original position; but
self-fertilisation afterw