Page:Popular Science Monthly Volume 74.djvu/588

584 North Atlantic slope. When the Weather Bureau can give as accurate measurements of the amounts of light reaching the soil in these different regions as of the temperatures, we shall see one reason for this difference. Even though flowers may be already formed, a certain though unknown amount of light is generally necessary to bring the flowers promptly to perfection. More than this, the number, size, color, fragrance and other qualities of the flowers, the number of eggs and sperm in them, even the formation of the flowers themselves, are dependent in very many plants upon an amount of light more than sufficient to maintain vigorous growth. This has been clearly shown by experiment on so many plants, simple and complex, as to lead one to think of light as a definite stimulus to reproduction. I can grow certain moss-like plants year after year in my laboratory and, according to their position, in a light or a dark place in the room, they will form reproductive organs or will remain sterile. I can do the same thing with submersed water-plants, and in garden and greenhouse the same fact is demonstrated year after year.

John Muir, in his "Mountains of California," gives the most glowing description of spring bloom which I know, where he tells of the San Joaquin Valley before it was settled. The newcomer to California to-day is struck with admiration of the great mats of color on hill-side and valley-floor. This prodigality of bloom far exceeds what one sees on either slope of the Alleghanies. Transplant the California "poppy" to any less sunny land and it degenerates; it blossoms less freely, its flowers are smaller, its petals are more sulphur or lemon than orange-yellow, its seeds are smaller and fewer. It seldom grows, still less blooms, under the shade of the live-oaks, though the open field may be golden with them. The more shade, the less bloom.

Testing this conclusion by experiment on plants very different in shape and size in their vegetative and reproductive stages, as is the case in Sempervirens and similar squat plants used for bedding or bordering, it has been found that the reproductive stage may be indefinitely postponed by growing the plant in feeble diffused light. Rather more light stimulates the plant to send up a stalk from its rosette of leaves, but this stalk is leafy. Still more light will induce the formation of flowers; but only when fully illuminated will the plant form perfect flowers and set good seed.

Cultivated violets are from eastern and European stock. In the middle west, in New England and in northern Europe, violets of many species form, in addition to the conspicuous blue flowers, others ordinarily concealed by the leaves. These hidden flowers are white or pale, lumpy, and closed. In certain districts in Italy, the same species of violet do not form these closed (cleistogamous) flowers. In the sunniest parts of California gardens the violets never form them. Other plants form cleistogamous flowers, but the number of these