233 



the experiineuts the lamp was suspended from the peak of the house, the arc being 

 1'^ feet above the soil of the beuch over which it was placed. * * 



During the first av inter (January to April, 1890) we used a 10 ampere, 45 volt, 

 Hrush arc lamp of 2,000 nominal candle ])ower. This was run all ni^lit — from dusk 

 until daylight — from January 23 to Ajtril 12. At lirst the light was started at 4:30 

 in the afternoon and ran until 7: 30 in the morning, but as the season advanced tin; 

 run was shortened, until in April it ran from 7 o'clock till 5. For the first 6 weeks 

 1 lie light was naked, but during the remainder of the time an ordinary white opal 

 globe was used. 



The experiments were in three series, (1) with a naked light running- 

 all night, (2) with a light protected with a white opal globe and rnn- 

 ning all night, (3) with a naked light running a part of the night. 



Experiments with a nalied lif/ht running all niglit. — These were with 

 radishes, carrots, endive, spinach, cress, lettuce, and peas. 



" The general effect of the light was to greatly hasten maturity, and 

 the nearer the plants gTew to the light the greater was the acceleration. 

 This tendency was particularly marked in the leaf plants — endive, 

 spina<ih, cress, and lettuce. The plants ' ran to seed ' before edible leaves 

 were formed, and near the light the leaves were small and curled." 



Details are given in notes and tables, and the results are illustrated 

 with cuts of specimen plants from both the light and dark houses. In 

 the case of lettuce it was observed that the plants did not increase in 

 size uniformly with the increase in distance from the lamjj. The lower 

 and higher plants alternated somewhat regularly, although there Mas 

 a general progression in height. "This alternating elevation and 

 depression is perhaps due to the concentric bands of varying intensity 

 of light which fall from the arc and which are caused by the uneven 

 burning of the carbons." 



In the case of endive " it chanced that for a time two rows gre^' par- 

 allel to each other in the light house, but one .stood in full light while 

 the other was shaded by an iron post 1.5 inches in diameter." At the 

 end of 2 months the plants in the row exposed to the full light aver- 

 aged 49.6 grains in weight, while those in the shaded row averaged 93.8 

 grains. 



In the dark house an average plant of the same age weighed 575 grains, 3.nd it 

 was larger leaved and darker colored than those grown in the other compart- 

 ment. * * * 



The young radish plants [on the highest bench] were strongly attracted by the 

 light, and in the mornirig they all leaned at an angle of from 60° to 45^ towards the 

 lamp. During the day they would straighten up, only to reach for the lamp again 

 on the succeeding night. This was repeated until the roots began to swell and tiic 

 jdant became stift'. As the plants grew, the foliage became much curled, and the 

 amount of this injirry was in direct proportion to the nearness to the lamj). Those 

 nearest the lamp (within 3 to 6 feet) were nearly dead at the expiration of 6 y ccks, 

 while those 14 feet away showed little injury to the leaves. 



The following figures rexu-esent the average weight in (miues ut rad- 

 ishes in the light and dark houses respectively: Entire plant, i).lt ind 

 1U;3;J0— 2so. 4 o 



