Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/104

84 the summit of one pillar in this latter flower, all the other pillars still stood upright and unbroken. I looked at the flowers of some surrounding plants, and everywhere found, as I had so often done before, broken-down pillars and masses of pollen on the stigmas.

From the usual state of the pillars of pollen, as well as from the gnawed condition of the ridges on the labellum, it may be safely inferred that insects of some kind visit the flowers, disturb the pollen, and leave masses of it on the stigmas. We thus see that the turning down of the distal portion of the labellum, by which a temporary landing-place and an open door are afforded,—the upturned labellum, by which the flower is made tubular so that insects are compelled to crawl close by the stigmatic surface,—the pollen readily cohering to any object, and standing in friable pillars protected from the wind,—and, lastly, the large masses of pollen above and below that layer of grains, the tubes of which alone penetrate the edge of the stigma,—are all co-ordinated structures, far from useless; and they would be quite useless if these flowers were always self-fertilised.

To ascertain how far the early penetration of the upper edge of the stigma by the tubes of those grains which rest on it, is effectual for fertilisation, I covered up a plant, just before the flowers opened, and removed the thin net as soon as they had begun to wither. From long experience I am sure that this temporary covering could not have injured their fertility. The four covered flowers produced seed-capsules as fine in appearance as those on any of the surrounding plants. When ripe, I gathered them, and likewise capsules from several of the surrounding plants, growing under similar conditions, and weighed the seed in a chemical balance. The seeds from the four capsules on the