At the time Siemens, in England, was conducting his experiments, Deherain was making investiga tions in Paris along the same line. He attempted to grow plants by continuous electric light, that is, with no daylight whatsoever. He found, as Sie mens did, that an unscreened light injured plants, although it promoted assimilation more effectively than a screened light. He found that barley, flax, chrysanthemums, pelargoniums, roses and others were severely injured after seven days of continu ous exposure to electric light, and that this injury was manifested by the dropping off or turning black of the foliage. In the case of lilacs, when the leaves were screened or protected by the upper leaves, no injury took place. Plants which received sunlight by day and electric light by night were injured in the same manner, but to a less degree. He found that electric light was far inferior to bright sunlight in its effects on photosynthesis, and that electric light was particularly injurious to seed lings, as most of them died before forming leaves. Deherain's conclusions are briefly as follows : Elec tric light contains rays harmful to vegetation. These, however, can be modified or eliminated by the use of transparent glass. It contains enough rays to maintain full-grown plants `a- months, but is too weak to enable seedlings to reach maturity.
Among those in America who have experimented with electric light are L. H. Bailey, of Cornell University, and F. W. Rane, formerly of the West Virginia Experiment Station. Bailey made exten sive experiments with the arc light, covering a period of four or five years. Bane, formerly Bailey's student, used the incandescent light. At first, Bailey employed a 2,000 candle-power un screened arc lamp suspended inside his forcing-house, and this was kept running all night. He made his experiments in a forcing-house 60 feet long and 20 feet wide, this being divided by a partition. In one part of the house, plants were exposed to an elec tric light at night, in addition to the daylight which they received, while the plants in the other part of the house were grown under normal conditions, receiving daylight only. According to his experiments the general effect of the electric light was to hasten maturity, and the nearer the plants were to the light the greater was the accelera tion, which was par ticularly marked in the case of crops like endive, spinach, cress and lettuce. He noticed a ten dency for the plants to run to seed, and the leaves which de veloped near the light became small and curl ed. The amount of starch in the leaves of both the electric and the non-electric plants was the same, al though the starch appeared to be more developed in those plants exposed to electric light. Lettuce plants within three feet of the lamp were killed outright soon after they came up, and the remaining plants were seriously injured, developing small, curled leaves.
The farther away the plants were from the light, the more vigorous they appeared, but they were not so vigorous as those grown in sunlight.
Radish plants made strong bendings toward the electric light ; their foliage curled and the injury was in direct proportion to the proximity of the lamp. Those plants located within three to six
feet of the lamp were nearly dead in six weeks, while those fourteen feet away showed little injury. The normal crops during the same length of time made twice the development of those subject to the electric light. Chemical analysis proved that there was more ash in them, twice as much potash, and the chlorophyll was somewhat more than in the normal plants. Nitrogen, however, was the same in both cases, but more amide nitro gen had been changed into other forms than in the normal plants, and those grown under an electric light were richer in albumenoids. Dwarf peas blossomed and fruited earlier but yielded only four sevenths as many seeds as those under normal con ditions, while the plants were considerably shorter in growth. Bailey found that carrots showed the least injury from the effects of the arc light.
The experiments just described were all made with a naked arc light ; but he further experi mented on the effects of screening the arc light with glass, in which case he made use of opal globes. This screening eliminated many of the ill effects brought about by the naked arc light ; while the loss in radishes from the use of the naked arc light was 45 to 65 per cent, with the screened light it averaged only 1 to 5 per cent. His results with lettuce were the most encouraging. This plant seemed able to adapt itself completely to screened light, while other plants, as before, showed a ten dency to run quickly to seed.
He then attempted to operate his electric light for only half the night, with the result that the foliage of radishes was noticeably larger. Peas, on the other hand. showed small leaves and less fruit under these conditions.
The most favorable results, however, were secured in the case of lettuce, when the house was lighted only half the night (Fig. 44). At the end of three weeks the lettuce plants under the influence of electric light were fully 50 per cent in advance of those in the normal house, and the color and other characteristics of the plants were equally good. The lighted plants had received about 70} hours of electric light during this period, and they were ready for the market one month later ; but it was six weeks before the plants in the normal house were equally developed. This forcing required 161t hours of electric light, at a cost amount ing to about $7. This experiment was repeated several times, with practically the same results. Further experiments showed that the injurious effects of electric light can be overcome by the interposition of glass, and good results were ob tained by suspending a lamp surrounded by a globe. Plants that were injured by the naked arc light hung inside the house, were benefited by the same light hung above the roof. Experiments were also made with colored screens. The practical con clusions which Bailey drew from his researches are that lettuce can be profitably forced by the use of the electric light, and that probably many flowers can be similarly benefited.