petals small, purplish, and in one species they are wanting; the axillary flowers of Bracenia purpurea are small and dull purple; in the common papaw the lurid purple flowers are large and adapted to Diptera, as are probably the lurid purple flowers of Calycanthus. Blue flowers may revert to red, white, or yellow. The fringed Polygala of Britain is usually bright blue, but often reverts to pink and white; there is a pure white variety of the blue-eyed grass; Mertensia virginica is purple-blue, rarely white; the larkspur is bright blue, sometimes white, and a white variety of the purple Trillium frequently occurs; there is, indeed, no improbability of a white-flowered form of every species being discovered. Viola calcarata is normally blue, but sometimes changes to the ancestral yellow.
The possession of a strong scent may, however, in many instances more than compensate for the absence of color. This is well illustrated in Lepidium sativum. The flowers are small and inconspicuous and in rainy weather do not fully open, yet, as it is odoriferous, Müller found it more abundantly visited by insects than any other crucifer. It is their strong odor, rather than their color, that renders so many umbellifers so attractive to a great variety of insects. Nocturnal flowers, which are visited by moths, are usually white and sweet-scented, though the evening primrose is yellow and Saponaria officinalis is rose-colored. Kohler and Schübeler have shown that a larger proportion of white flowers are fragrant than of any other color. Of 1,193 white flowers examined by them, 187 were odoriferous; of 951 yellow, 75; of 923 red, 85; of 594 blue, 31. But neither color nor odor will long alone serve to insure the visits of insects. The common elderberry exhibits the disadvantages which may attend the want of honey when there is but a limited supply of pollen. There are great masses of odoriferous flowers which convert the shrub into a huge bouquet, but it blooms at mid-summer, when it must contend with many nectar-yielding plants. As a result, it is almost wholly deserted by insects. Only four species of flies have been taken upon it, and repeatedly the blossoms were examined without discovering a single visitor, and yet upon the jewel-weed and the red-osier cornel, a few yards away, scores were at work.
