Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/87

. II. of the bristle. They then quickly become depressed so as to lie in the same line with the bristle,—one a little on one side, and the other on the other side; and if the bristle, held in the same relative position, be now inserted into the nectary of another flower, the two ends of the pollinia accurately strike the two protuberant stigmatic surfaces, situated on each side of the mouth of the nectary.

The flowers smell sweet, and the abundant nectar always contained in their nectaries seems highly attractive to Lepidoptera, for the pollinia are soon and effectually removed. For instance, in a spike with forty-five open flowers, forty-one had their pollinia removed, or had pollen left on their stigmas: in another spike with fifty-four flowers, thirty-seven had both pollinia, and fifteen had one pollinium, removed; so that only two flowers in the whole spike had neither pollinium removed.

My son George went at night to a bank where this species grows plentifully, and soon caught Plusia chrysitis with six pollinia, P. gamma with three, Anaitis plagiata with five, and Triphæna pronuba with seven pollinia attached to their proboscides. I may add that he also caught the first-named moth in my flower-garden, with the pollinia of this Orchis attached to its proboscis, but with all the pollen-grains removed, although the garden is a quarter of a mile distant from any spot where the plant grows. Many of the above moths had only a single pollinium attached, somewhat laterally to their proboscides; and this would happen in every case, unless the moth stood directly in front of the nectary and inserted it proboscis exactly between the two discs. But as the labellum is rather broad and flat, with no guiding ridges like those on the labellum of Orchis pyramidalis, there is nothing to