LIGHT AND LIFE. 299 



botanist, Prillieux, published the result of a course of experiments 

 made with an entirely different purpose, and taking up the study of 

 the action of light from a new point of view. Resting on the twofold 

 consideration that the distinctly-colored rays are not equally luminous, 

 and that those of the greatest illuminating power are also those which 

 act with most energy on plants, Prillieux undertook to examine what 

 influence will be exercised on plants by rays different in color, but 

 known to be equal in intensity, and whether this influence differs in 

 the case of different colors, or is the same, provided they do not vary 

 in illuminating power. The long and conscientious researches of this 

 experimenter led him to the conclusion, that rays of different colors 

 act with equal force on the green parts of plants, and produce an equal 

 release of gas, when they have the like luminous intensity. He holds 

 that all luminous rays effect the reduction of carbonic acid by vege- 

 tables in proportion to their illuminating power, whatever their refran- 

 gibility may be. If the yellow and orange rays are more active in 

 this respect, it is because their luminous glare is much greater than 

 that of the extreme rays. 



The luminous rays also promote the production of green tissue, the 

 green matter of all vegetables. Gardeners blanch certain plants by 

 raising them in the dark. They thus obtain plants of a pale yellow, 

 spindling, without strength or crispness. They are attacked by a true 

 chlorosis, and waste away, as if sprung from barren sand. The sun 

 also aids the transpiration of plants, and the constant renewal of 

 healthy moisture in their tissues. On failure of the evaporation of 

 moisture, the plant tends to grow dropsical, and its leaves fall, from 

 weakness of the stem. 



This love of plants for light, which is one of the most imperious 

 needs of their existence, displays itself also in other interesting phe- 

 nomena, which show that solar rays are, in very truth, the fertilizer 

 that produces color. The corolla of vegetable species growing at great 

 heights on mountains has livelier colors than that of species that spring 

 in low spots. The sun's rays, in fact, pass more easily through the 

 clear atmosphere that bathes high summits. The hue of certain flow- 

 ers even varies according to the altitude. Thus the corolla of the An- 

 tliyllis vulneraria shades down from white to pale red and vivid pur- 

 ple. In general, the vegetation of open, well-lighted places is richer in 

 color and development than that of regions not accessible to the sun. 

 Some flowers originally white afterward deepen in color by the direct 

 action of light. Thus Cheiranthus cameleo has a flower at first whitish, 

 afterwai'd yellow, and, at last, a violet-red. The Hibiscus mutabilis 

 bears a flower which opens at morning with a white hue, and grows 

 red during the day. The flower-buds of the Agapanthus umbellatus 

 are white when they begin to unclose, and afterward take on a blue 

 tint. If, at the moment of leaving its spathe, the flower is wrapped in 

 black paper, intercepting the light, it remains white, but regains its 



