584 THE POPULAR SCIENCE MONTHLY 



North Atlantic slope. When the Weather Bureau can give as accurate 

 measurements of the amounts of light reaching the soil in these differ- 

 ent 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, accord- 

 ing 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 Cali- 

 fornia 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 Cali- 

 fornia " 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 in- 

 definitely postponed by growing the plant in feeble diffused light. 

 Eather 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 



