There is scarcely any subject to which Darwin devoted so much time and work as to his researches into the biology of flowers, or, in other words, to the consideration of the question to what extent the structural and physiological characters of flowers are correlated with their function of producing fruits and seeds. We know from his own words what fascination these studies possessed for him. We repeatedly find, for example, in his letters expressions such as this:— “Nothing in my life has ever interested me more than the fertilisation of such plants as Primula and Lythrum, or again Anacamptis or Listera.”

Expressions of this kind coming from a man whose theories exerted an epoch-making influence, would be unintelligible if his researches into the biology of flowers had been concerned only with records of isolated facts, however interesting these might be. We may at once take it for granted that the investigations were undertaken with the view of following up important problems of general interest, problems which are briefly dealt with in this essay.

Darwin published the results of his researches in several papers and in three larger works, (i) On the various contrivances by which British and Foreign Orchids are fertilised by insects (First edition, London, 1862; second edition, 1877 ; popular edition, 1904). (ii) The effects of Cross and Self fertilisation in the vegetable kingdom (First edition, 1876 ; second edition, 1878).