RESPONSE OP PLANTS TO ARTIFICIAL LIGHTS 



23 



period of four or five years. Rane, 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 curled. The 

 amount of starch in 

 the leaves of both 

 the electric and the 

 non-electric plants 

 was the same, al- 

 though the starch 



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- 



Fig. 44. Lettuce of the same age £ind variety grown under normal conditions of sunlight (above) 

 and with naked electric arc light running part of the night in addition (below) , five weeks 

 after planting in permanent quarters. (Bailey.) 



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 bondings 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 



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 



