154 Agricultural Experiment Station, Ithaca, N. Y. 



the rays lying between red and yellow, about seven per cent of the 

 yellow rays, while all the blue rays were cut off. Amber transmitted 

 about forty per cent of the orange rays, with a very small per cent of 

 the green and none of the blue. The plain or white glass transmitted 

 eighty per cent of the red rays, and sank to about seventy per cent of 

 the blue rays. A portion of this color screen may be seen in the upper 

 left corner of Plate I. 



The first year's experiment was started late in winter, and little was 

 learned from it except the proper methods of conducting the investiga- 

 tion. Trays of germinating radish seeds, in soil, were placed in the 

 various fields at equal distances from the arc, and the behavior of the 

 young plants was watched with interest. March 12, 1892, the plants 

 being from one to three inches high and in seed-leaf, marked helio- 

 tropism was noticed in the morning, even when the light had stopped 

 burning at 1 1 o'clock the previous evening. In the naked light the 

 young plants pointed strongly tojvards the lamp. The red and white 

 lights produced a little effect in drawing the plants towards the lamp, 

 Avhile in the blue field the effect was scarcely perceptible and in the 

 orange field it was none. On the morning of March thirteenth, the 

 results were about the same, except that the red and white lights 

 seemed to have had more effect than on the previous night. It was 

 apparent that the smallest plants were those in the orange light. The 

 next night the light burned but a short time, and on the following 

 morning the plants all looked towards the sunlight. On the fifteenth, 

 the heliotropism towards the lamp was again marked. The best plants 

 were those in the naked light and the poorest those in the orange light. 



On the 7th of November, 1892, lettuce plants, for which the seed 

 had been sown October third, were set in a ground bed eight feet wide 

 and twenty-three feet long. A week later, the electric lamp, sur- 

 rounded by the color screen, was hung in front of this bed, four feet 

 above it and three feet from it. The light burned about five hours 

 each night, usually from 5 o'clock until 11. December first there was 

 no difference in the plants under the various lights, and the lamp was 

 then transferred to the opposite side of the bed and hung only a foot 

 and a half above it, as shown in Plate I. This change was made in 

 order to bring the light nearer to the plants and also to bring all the 

 five screens to bear upon the crop. In the former position only the 

 red, blue and orange screens threw light upon the plants, the plain 

 glass and naked sections being out of range of the bed. The position 

 of the screens was also reversed in changing the lamp, save the blue, 

 which occupied the middle portion of the frame. The light now began 



