This section is from the book "On British Wild Flowers Considered In Relation To Insects", by John Lubbock. Also available from Amazon: Nature Series On British Wild Flowers Considered In Relation To Insects.
This order contains two British genera: Utricularia and Pinguicula. Both are fertilised by insects, and in both the insect first touches the stigma, and afterwards comes in contact with the stamens. In Utricularia the stigma is irritable and retracts at once on being touched, so that the proboscis after dusting itself with the pollen does not again come into contact with it.
Both genera are insectivorous. Utricularia is aquatic, and the submerged leaves bear small bladders or utricles, at the entrance of which are stiff hairs so arranged as to permit the entrance, but prevent the exit of small water animals. Even fish, of course only when very young, are sometimes so captured.
In Pinguicula the leaves are covered with sticky, glandular hairs, and the escape of any small flies or other insects which may be so unfortunate as to alight on them is rendered more difficult by the fact that the edges are curved over.
In Vinca (the Periwinkle), which has been described by Delpino and Hildebrand, the arrangement resembles in principle that already described in Polygala. The anthers and the stigma, which is immediately below them, together nearly close up the tube of the flower. The upper portion of the pistil is clothed with hairs which arrange themselves so as to form a sort of pocket or chamber opposite each anther, and when the pollen is shed it is received into this pocket or chamber. The stigma somewhat resembles an inverted saucer, attached by the middle to the style. The upper portion of the stigma is viscid and rubs against the proboscis of the insect as it is withdrawn. The proboscis, thus rendered adhesive, carries off some of the pollen. When the insect visits the next flower, the pollen is scraped off the proboscis by the sharp edge of the saucer, and is thus accumulated in the hollow of the saucer, which is the true stigmatic surface.
In this order we have six British genera: Cicendia, Erythmea, Gentiana, Chlora, Menyanthes, and Lim-nanthemum.
Gentiana Pneumonanthe is proterandrous. It secretes honey at the base of a tube 25 - 30 mm. long; Bees, however, can creep half way down, in doing which they come in contact with the anthers in younger flowers, and in older ones with the stigma, which lies somewhat higher in the tube. The power of self-fertilisation appears to be lost. Gentiana ama-rella, on the contrary, is homogamous, the anthers and stigma coming to maturity together, though as the style of pistil is somewhat longer than the stamens, an insect touches the stigma before reaching the anthers.
The beautiful Erythraea centanrium is frequently visited by butterflies, though it contains no honey, at least neither Sprengel nor Muller could find any. Menyanthes and Limnanthemum (Kuhn, "Bot Zeit," 1867) are said to be dimorphous.
This family is represented in England by one species, Polemoniiim cceruleum, and even this is a doubtful native. It has been shown by Axell to be proterandrous.