THE ORIGIN OF FLOWERS Introduction--Precursors of Darwin--Pollination by wind--Arrangements in flowers for securing cross-fertilization--Salvia, Pedicularis--Flowers visited by flies--Aristolochia--Pinguicula--Daphne--Orchids--Flowers are built up of adaptations--Mouth-parts of insects--Proboscis of butterflies--Mouth-parts of the cockroach--Of the bee--Pollen baskets of bees--Origin of flowers--Attraction of insects by colour--Limitation of the area visited--Nägeli's objection to the theory of selection--Other interpretations excluded--_Viola calcarata_--Only those changes which are useful to their possessors have persisted--Deceptive flowers--Cypripedium--Pollinia of Orchis--The case of the Yucca-moth--The relative imperfection of the adaptations tells in favour of their origin through natural selection--Honey thieves. WHEN one species is so intimately bound up with another that neither can live for any length of time except in partnership, that is certainly an example of far-reaching mutual adaptation, but there are innumerable cases of mutual adaptation, in which, although there is no common life in the same place, yet the first form of life is adjusted in relation to the peculiarities of the second, and the second to those of the first. One of the most beautiful, and, in regard to natural selection, the most instructive of these cases is illustrated by the relations between insects and the higher plants, relations which have grown out of the fact that many insects have formed the habit of visiting the flowers of the plants for the sake of the pollen. In this connexion the theory of selection has made the most unexpected and highly interesting disclosures, for it has informed us how the flowers have arisen.