Red flowers are much rarer than blue, and both are seldom common in the same family. For instance, in the pink family red and white blossoms prevail, and there are no blue shades. The pinks are crimson and scarlet, often with elegant markings and a strong aromatic odor. The honey is deeply concealed, and they are visited almost exclusively by butterflies and millers. Twenty-eight species of diurnal Lepidoptera have been collected upon a single variety of Saponaria. Of the eighty species of Rosaceæ, thirteen are red and two purple, but the forty-four white flowers are very generally tinged or tipped with red. The two purplish-flowered species, Geum rivale and Potentilla palustris, belong to genera in which yellow predominates, and this primitive color is still evident in both their calyx and corolla. There are no blue or violet flowers. This family exhibits a marked tendency both in stem, leaf, bud, flower, and fruit to develop reddish coloration, a tendency which is probably due to the chemical constitution of the sap. There are no flowers in this family adapted to Lepidoptera, but they are visited by a mixed company of flies, beetles, and Hymenoptera. The smaller and less specialized Rosaceæ are yellow and white and are visited by a variety of short-lipped insects. With the increase of the flower in size and conspicuousness the number of insect visitors greatly increases, and the enlargement of the flower is attended by red coloration. Owing to the chemical constitution of the nutritive fluid, probably to its acidity (for when the petals of a rose are treated with ammonia they become blue), there has been no opportunity for the development of blue coloration by insects. With the enlargement of the perianth and the increased flow of sap, red tints have tended to appear by process of oxidation.
The correlation of red coloring with an increased flow of sap is well illustrated by the galls of the wild-rose tree, which are often "as rosy as the rosiest apple." An abnormal flow of sap is caused to the part stung by the insect, and red coloration is due to the action of light, for it is of no service to the plant. Again, when the flowers of Cratægus coccinea are stung by the gall-fly the different organs all become bright red, and the change in coloring is accompanied by an increase in size. In some instances red colors, according to Darwin, indicate greater vigor on the part of the plant, and I have also observed that the dwarfing of red flowers under cultivation may cause them to revert to white.
It was long, indeed, believed that the same species could not produce yellow, red, and blue flowers. But this doctrine, to use the words of Dr. Lindley, "must now be laid up in the limbo of pleasant 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 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 midsummer, 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.
Among the more recent applications of electricity is one for the desiccation of wood, by the Nadon Bretonneau method, by which wood is made as fit for use for certain exact processes in as many months as it has formerly taken years. It is also proposed by Mr. Shaw, an English mining engineer, to substitute water and steam for gunpowder in mine blasts, a cartridge of water being placed instead of the powder cartridge, and vaporized by passing the electrical current through it.