26 



RESPONSE OF PLANTS TO ARTIFICIAL LIGHT 



following the use of the incandescent gaslight and 

 the incandescent electric light as well, as gathered 

 from these experiments, is from their richness in 

 red and orange rays. A summary of the results of 

 Corhett's work showed : 



(1) The incandescent gaslight of the Welsbach 

 burner was an active stimulus to plant growth 

 when used at night to supplement daylight. 



Fig. 46. Plants grown wholly by acetylene ligbt, with no sunlight. 



(2) Lettuce plants subjected to the influence of 

 the incandescent gaslight at night were taller and 

 heavier than plants of the same variety and seed- 

 sowing grown in normal conditions. 



(3) Lettuce and spinach subjected to the stimu- 

 lating influence of the light grew faster and com- 

 pleted their growth in less time than plants of the 

 same sorts from the same seed-sowing grown in 

 normal conditions. 



(4) No injurious effects resulted from the use of 

 the incandescent gaslight. 



(5) The stimulating influence of the light as indi- 

 cated by the growth of plants used in various tests 

 is shown by the order in which the sorts are named, 

 the flrst being the most susceptible — spinach, cab- 

 bage, radish, lettuce, tomato. 



(6) The range of the light was somewhat vari- 

 able for the different crops. In general, the maxi- 

 mum growth was attained at twelve to sixteen 

 feet from the light, while a perceptible increase 

 was noted at twenty-four feet. 



(7) Bloom record of tomatoes showed markedly 

 earlier bloom in the light house, — eight days the 

 least and eighteen days the greatest difference. 



(8) In the case of radishes, top growth was stim- 

 ulated, but evidently not markedly, at the expense 

 of root. With sugar-beets, top growth was greatly 

 stimulated, evidently at the expense of root 

 growth. 



(9) While the roots of beets grown in the nor- 

 mal house were larger than those in the light 

 house, the sugar contents and the percentage of 

 purity were markedly higher in the light-house 

 grown plants. 



(10) Spinach, lettuce and radishes all tended to 

 make seed-stalks earlier under the light. 



(11) Lettuce and spinach under the influence of 

 the incandescent gaslight not only grew faster 

 during the growing period, but the period was 

 actually longer than for plants in the normal 

 house. 



The Cooper-Hewitt mercury vapor electric light. 



C. P. Close, of the Delaware Experiment Station, 

 endeavored to determine the effect 

 of the Cooper-Hewitt mercury vapor 

 electric light on plants. The re- 

 sults of his work were presented 

 before the Society for Horticul- 

 tural Science, at its second annual 

 meeting, and are recorded in the 

 proceedings of the society. 



In conducting this test it was 

 necessary to have an enclosed place 

 practically light-tight, so as to ex- 

 clude the daylight and allow the 

 plants to have the artificial light 

 only. This was provided by build- 

 ing in the greenhouse a "double- 

 deck " bed, using the upper bed for 

 plants in sunlight and the lower 

 bed for those in artificial light. The 

 lamps used were the Cooper-Hewitt 

 4-H pattern. These were suspended 

 as nearly over the center of the 

 bed as possible. Owing to variation in the electri- 

 cal potential — from 100 to 125 volts — a constant 

 intensity oflight could not be maintained. 



The light from these lamps is perfectly white, 

 devoid of red rays. The candle-power of 'a 4-H 

 lamp, or tube, is about 650, and the expense per 

 candle-power is about one-eighth that of the candle- 

 power of the incandescent electric light, and about 

 three-fourths that of the arc light. The light is 

 caused by the vapor of mercury in the tube becom- 

 ing heated white hot as the electric current is 

 passed through it. One end of the lamp-tube is 

 positive, the other negative, and the vapor of mer- 

 cury completes the circuit by connecting the two. 

 Tests were made with lettuce and radishes. Over 

 the lettuce at first only one lamp was used, placed 

 about sixteen inches from the soil. The growth was 

 unsatisfactory because of the unfavorable tem- 

 perature and atmospheric conditions of the bed, due 

 to the tight enclosure, allowing no ventilation. 

 The excess of moisture that accumulated in the 

 atmosphere was a great hindrance. The plants 

 received light only during the night. They partook 

 of the nature of twining plants. The stems were 

 long and produced leaves at intervals of two or 

 three inches ; and not being strong enough to sup- 

 port their weight, assumed a recumbent position. 

 It was impossible to keep plajits alive for any 

 length of time when they were more than two or 

 three feet beyond the end of the lamp-tube. The 

 time for germination was the same as for seed 

 sown in daylight. The formation of chlorophyll 

 seemed to be perfectly normal. After a few weeks 

 the plants came practically to a standstill. With 

 two lamps, the results were but little more en- 

 couraging. 



