Page:Popular Science Monthly Volume 55.djvu/711

Rh dreams." This supposed law is contradicted by the hyacinth, pansy, Delphinium cardinale, and many other plants. Though red and blue coloring never occurs among the roses, a hyacinth has been seen to produce a perfectly pink and a perfectly blue blossom on the same truss, and the Borraginaceæ afford examples of flowers turning from red to blue in even a short space of time.

Blue is the highest color of the floral world, and is preferred by bees. Blue flowers are, as a rule, highly specialized both in form and color, and often possess marvelous mechanisms which aid in disseminating the pollen. This coloring is very common in the mint and pulse families, and in this district there are in the former forty-nine and in the latter sixty-one species of blue flowers. Their structure is such that few insects besides the long-tongued bees can gain access to the honey, and in some instances a single species of flower is visited by a single kind of bee, as one of the larkspurs by one of the bumblebees. While this high specialization of the flower may insure intercrossing, it is yet open to many objections, such as scarcity of proper guests, mechanical imperfections, perforation of the flowers by bees, and development of the perianth at the expense of the essential organs.

It is noteworthy that when genera occur containing three or more species they are seldom all blue or purple; one species at least, and frequently more than one, is yellow, white, or red. In Trifolium, T. pratense is rose-purple, T. repens white, and T. agrarium yellow. In the genus Astragalus a part of the species are violet or blue and a part white, and the same is true of Lespedeza and Vicia; in Lathyrus three species are blue-purple, one yellow, and one yellowish white. It is probably more advantageous in these genera for a part of the species to be of one color and a part of another than for all to be blue. When species are closely allied bees tend to visit them indiscriminately, as has been observed to be true of the buttercups, Spiræas, and golden-rods. During an afternoon the writer carefully collected the insect visitors to Solidago bicolor, our only cream-colored golden-rod. Both the number of species and of individuals taken was much larger than upon the yellow-flowered and more abundant varieties of this genus growing near by. There could be no doubt that the whitish coloration was beneficial in enabling insects to distinguish it more readily. Many purplish flowers are regular, often showing indications of degeneration, are devoid of honey, and are self-fertilized or adapted to Diptera, or, as in Hepatica, which is visited by bees for the pollen, open to a wide circle of visitors. In the sea purslane (Sesuvium maritimum), a prostrate maritime herb, there are no petals, but the five-parted calyx is purplish inside. The genus Ammannia of the Lythraceæ has the