Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/109

. III. flowers in a withered condition, and seventy-one of these had pollen on their stigmas, and only twenty-eight had all four pollinia still within their anthers. All the New Zealand species bear solitary flowers, so that distinct plants cannot fail to be intercrossed. I may add that Mr. Fitzgerald also placed a small beetle on the labellum of P. longifolia, which was instantly carried into the flower and imprisoned; afterwards he saw it crawl out with two pollinia attached to its back. Nevertheless he doubts, from reasons which seem to me quite insufficient, whether the sensitiveness of the labellum is not as great a disadvantage as an advantage to the plant.

Mr. Fitzgerald has described another Orchid belonging to the same sub-tribe, Caladenia dimorpha, which has an irritable labellum. He kept a plant in his room, and says: "A house-fly lighting on the lip was carried by its spring against the column, and becoming entangled in the gluten of the stigma, and struggling to escape, removed the pollen from the anther and smeared it on the stigma." He adds, "Without some such aid the species of this genus never produce seed." But from the analogy of other Orchids we may feel sure that insects usually behave very differently from the fly which he saw caught on the stigma, and no doubt they carry the pollen-masses from plant to plant. The labellum of another Australian genus, Calæna, one of the Arethuseæ, is said by Dr. Hooker to be irritable; so that when touched by an insect it shuts up suddenly against the column, and temporarily encloses its prey as it were within a box. The labellum is covered by curious papillæ, which, as far as Mr. Fitzgerald has seen, are not gnawed by insects.