CHAPTER IX.

THE EFFECTS OF CROSS-FERTILISATION AND SELF-FERTILISATION ON THE
PRODUCTION OF SEEDS.

Fertility of plants of crossed and self-fertilised parentage, both lots
being fertilised in the same manner.--Fertility of the parent-plants
when first crossed and self-fertilised, and of their crossed and
self-fertilised offspring when again crossed and
self-fertilised.--Comparison of the fertility of flowers fertilised with
their own pollen and with that from other flowers on the same
plant.--Self-sterile plants.--Causes of self-sterility.--The appearance
of highly self-fertile varieties.--Self-fertilisation apparently in some
respects beneficial, independently of the assured production of
seeds.--Relative weights and rates of germination of seeds from crossed
and self-fertilised flowers.


CHAPTER X.

MEANS OF FERTILISATION.

Sterility and fertility of plants when insects are excluded.--The means
by which flowers are cross-fertilised.--Structures favourable to
self-fertilisation.--Relation between the structure and conspicuousness
of flowers, the visits of insects, and the advantages of
cross-fertilisation.--The means by which flowers are fertilised with
pollen from a distinct plant.--Greater fertilising power of such