154 



AMERICAN HOMES AND GARDENS 



April, I 910 



The Effect of Colored Light on Vegetation 



By Frank Brown 



FLAM MARION for many years has been the house with colorless glass had attained a height of 

 studying the effects of sunlight upon \ege- four inches, and the plants under green glass had reached 

 tation. In his early experiments he had that of six inches. But the most remarkable growth had 

 the assistance of M. Georges Mathieu, been made in the red house, where the average height of 

 and he is now working in collaboration the plants exceeded sixteen inches. Moreover, the sensi- 

 with M. Julien Loisel, at .the agricultural tiveness of the plants in the red house was increased to 

 station of Juvisy, near Paris. such a degree that the slightest movement or the lightest 



In order to carry out these researches, which extend breath of air caused their leaves to close and even whole 

 over considerable periods of time, he constructed four small branches to droop. The plants in the blue house, on the 

 forcing houses enclosed with glass. The glass of one house, contrary, had almost completely lost their sensitiveness, 

 which is used to establish the effect of the total solar radia- Similar, though less marked effects were observed with 



tion as a standard of comparison, is colorless, and the begonias, geraniums, pansles, strawberry plants, oak seed- 

 other houses are glazed with red, green and dark blue lings, etc. In the blue house, strawberries remained edible, 

 glass respectively. All these colored glasses are very and almost unchanged from May to October. This result 

 nearly monochromatic, as was proved by a careful exami- is of great practical importance, for it indicates the possi- 

 nation with the spectroscope. Thus the experiments were bility of accelerating or retarding the growth of vegetables 

 conducted in three well-separated regions of the solar spec- and the ripening of fruits by the employment of red or 



blue glass. The variously 

 colored rays affected oaks 

 somewhat differently from 

 the other plants. The seed- 

 lings exposed to red light 

 made the most rapid 

 growth of all, but the 

 plants in the blue house 

 grew more rapidly than the 

 plants under either green 

 or white glass. 



■\corns v/ere planted in 

 pots, at a uniform depth of 

 one and a half inches, on 

 March 6, 1905, and ten of 

 the pots were placed in 

 each of the four houses. 

 Five plants made their ap- 

 pearance in the white, and 

 the same number in the 

 red, house, but only three 

 in the blue and two in the 

 green. On September 26, 

 1906, the average heights 

 in inches of the plants in 

 he various houses were as 

 follows: Red, 17X'! blue, 

 io>^ ; white, 6>^ ; green, 

 414- Thus the plants un- 

 der red glass were four 

 times as high as the plants 

 under green glass. Fur- 

 thermore, at the end of 

 February, 1907, all the 

 foliage ot the oaks in the 

 white house had turned 

 yellow, while only a few 

 leaves had turned in the 

 red house, and the foliage 

 of the young trees in the 

 green and blue houses re- 

 mained bright green. In 

 October, 1907, the colors 

 of the foliage in all the 

 houses remained as they 

 were in February. The 

 growth of male ferns ex- 



trum : the red end, the 

 middle of the green nearly 

 coincident with the color of 

 the foliage of most plants, 

 and the extreme blue just 

 within the violet. This 

 last color was selected be- 

 cause it was impossible to 

 obtain violet glass of suffi- 

 ciently good quality. 



The four houses are 

 placed side by side, as 

 shown in the photograph, 

 in identical meteorological 

 conditions. In order to as- 

 sure uniformity of tem- 

 perature, each house is 

 provided with \'entilating 

 pipes, so arranged that the 

 air moves from south to 

 north, and no light is ad- 

 mitted through the ventila- 

 tors. 



In general, it was found 

 by M. Flammarion and his 

 assistants that growth is 

 promoted by red light. 

 This fact was established 

 in regard to plants belong- 

 ing to families widely sep- 

 arated in the botanical 

 series, from sensitive plants 

 and lettuce, to begonias 

 and oaks. 



Blue light, on the other 

 hand, exerted scarcely any 

 effect. For example, sensi- 

 tive plants of the same age 

 and height — about one inch 

 — were planted in the four 

 houses on August ist. 

 Three months later the 

 blue house plants had hard- 

 ly grown, though they 

 continued to live in a latent 

 and sluggish fashion. 

 Meanwhile the plants in 



Oak seedlings raised under glass of various colors. 



Begonia plants raised under glass of various colors. 



