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.