compelling insects to visit the flowers in front. Few persons now doubt the correctness of C. K. Sprengel's view,[1] that the bright and conspicuous colours of flowers serve to attract insects from a distance. Nevertheless some Orchids have singularly inconspicuous and greenish flowers, perhaps in order to escape some danger; but many of these are strongly scented, which would equally well serve to attract insects.
The labellum is by far the most important of the external envelopes of the flower. It not only secretes nectar, but is often modelled into variously shaped receptacles for holding this fluid, or is itself rendered attractive so as to be gnawed by insects. Unless the flowers were by some means rendered attractive, most of the species would be cursed with perpetual sterility. The labellum always stands in front of the rostellum, and its outer portion often serves as a landing-place for the necessary visitors. In Epipactis palustris this part is flexible and elastic, and apparently compels insects in retreating to brush against the rostellum. In Cypripedium the distal portion is folded over like the end of a slipper, and compels insects to crawl out of the flower by one of two special passages. In Pterostylis and a few other Orchids the labellum is irritable, so that when touched it shuts the flower, leaving only a single passage by which an insect can escape. In Spiranthes, when the flower is fully mature, the column moves from the labellum, space being thus left for
- ↑ This author's curious work, with its quaint title of 'Das Entdeckte Geheimniss der Natur,' until lately was often spoken lightly of. No doubt he was an enthusiast, and perhaps carried some of his ideas to an extreme length. But I feel sure, from my own observations, that his work contains an immense body of truth. Many years ago Robert Brown, to whose judgment all botanists defer, spoke highly of it to me, and remarked that only those who knew little of the subject would laugh at him.
