PHYSICAL AND METEOROLOGICAL RESEARCHES. Ill 



a convex lens placed between the prism and the arc lamp. These were 

 placed at a distance from the prism equal to double that of the focus 

 of the lens The prism was placed in the position of least deviation to 

 the spirits of turpentine, which was in this case 30°. The spectrum 

 reflected upon a screen .'i meters from the prism measured about 25 

 cm. (nearly 10 in.) in length. The arc light gave a constant intensity 

 of 10 amperes and burned twenty hours daily. Notwithstanding- the 

 limited size of the spectrum a series of experiments was started, which 

 permitted the verification of the results obtained in the colored hot- 

 houses. These experiments were on the growth of flax and vetches, 

 and on the transpiration of leaves. 



August 25 a small box of flax was exposed to the luminous region of 

 the spectrum. The plants had sprouted and reached a height of 0.04 

 meter, and the cotyledons were slightly expanded. On August 27 the 

 first leaves were beginning to expand in the red portion of the spectrum, 

 and some leaves appeared in the yellow, but no change was observed at 

 the right end of the spectrum. On September 4, ten days after the 

 beginning of the experiments, the box with the plants was photographed 

 and the plants were measured. In the red light the stems had attained 

 a height of 0.085 meter, and in the blue 0.040 meter. 



The temperature remained the same for all plants during the time of 

 experiment; it varied between 10° and 30°, with an average temper- 

 ature for the ten days of 18° O. On account of great difficulties encoun- 

 tered the experiments had to be discontinued. They were continued far 

 enough to verify the favorable action of the red rays upon the growth 

 of plants. This favorable action seems to be due partly to the infra red 

 rays. The pure green of the spectrum was very small, and on this ac- 

 count plants exposed to green rays received some yellow rays. The use 

 of carbon bisulphid would have provided a more extensive spectrum. 



The common vetch ( Vicia communis) is very sensitive to light, and 

 grows very rapidly under a weak illumination. Pots of three plants 

 each were placed in different portions of the spectrum and separated by 

 small black screens At the commencement of the experiment their 

 height was 0.04 meter. The average height of the plants in each pot 

 August 15 was as follows: Bed 0.09, yellow 0.08, green 0.05, violet 0.07; 

 and August 20, red 0.21, yellow 0.185, green 0.16, violet 0.15 meter. 

 As in the other cases, the maximum growth took place in the red por- 

 tion of the spectrum, the results obtained witli the spectrum of the elec- 

 tric light and in the hothouses with colored glasses agreeing. 



EFFECT OF WHITE AND COLORED LIGHT ON TRANSPIRATION. 



In the course of the above experiments the transpiration of the leaves 

 under different rays of the spectrum was measured. It was found that 

 grapevines attained the maximum of transpiration in white light, there 

 being a decrease from red to bine. An experiment on leaves of maize 

 exposed to different regions of the luminous electric spectrum gave 

 4485— No. 2 2 



