--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
pollen.--Anemophilous species.--Conversion of anemophilous species into
entomophilous.--Origin of nectar.--Anemophilous plants generally have
their sexes separated.--Conversion of diclinous into hermaphrodite
flowers.--Trees often have their sexes separated.
CHAPTER XI.
THE HABITS OF INSECTS IN RELATION TO THE FERTILISATION OF FLOWERS.
Insects visit the flowers of the same species as long as they
can.--Cause of this habit.--Means by which bees recognise the flowers of
the same species.--Sudden secretion of nectar.
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