Note 52 — VII. BY-PATHS IN THE DOMAIN OF BIOLOGY:

The probable influence of fertilization by birds on the flowers of the Auckland Isles has been referred to at p. 238. Mr. Darwin, in his book on Cross and Self-Fertilisation of Plants (p. 371), gives in a note numerous cases in which birds are known to fertilise flowers, the most important being that of several species of Abutilon in South Brazil, which, according to Fritz Müller, are sterile unless fertilised by humming-birds. This proves, not only that birds fertilise flowers in the same manner as insects, but that the two classes of organisms have become so correlated as to be mutually necessary to each other; and it completely justifies us in imputing the fertilization of flowers to flower-frequenting birds wherever these are present and suitable insects are notoriously scarce, as is the case in so many of the islands here referred to.