XOVKMBEK G, 1903.] 



SCIENCE. 



605 



effects of the screens mentioned, a number of 

 metal frames were made so as to admit of 

 free insertion of any of the plates into any of 

 the four vertical sides of the frame. The 

 plant to be used in the test was placed within 

 the frame and enclosed on two opposite sides 

 by opaque screens, and on the other two ver- 

 tical sides were placed plates of two different 

 ' colors.' On the top and the bottom were 

 opaque plates. Then the plant was enclosed 

 within the ' lantern ' and placed equally dis- 

 tant from the two color-screens. No light 

 was admitted to the plant excepting that 

 coming through the two screens; and, since 

 the top was covered, the plant was subjected 

 to lateral illumination from two different 

 ' colors ' at the same time and from opposite 

 directions. Care was taken to have only dif- 

 fused daylight enter the screens and to have 

 it equal in intensity. Now it seemed reason- 

 able to conclude that if curvature of the stem 

 of the plant took place toward one of the col- 

 ored screens, the light which penetrated that 

 screen produced most phototropic stimulus. 

 The lanterns, not being actually air-tight, per- 

 mitted the plant to live under more natural 

 conditions of temperature, moisture and air 

 than could be obtained by means of a double 

 bell-jar. 



The results obtained are sunmiarized as 

 follows and are represented by the curve given 

 in Fig. 2, I. They rank in order named : blue, 

 white (window glass), violet, green, yellow, 

 red, dark (opaque). Between certain pairs of 

 these screens the difference is not very great, 

 but there is a positive difference in every case. 



The main differences between these results 

 and those of Wiesner, Guilleman and Sachs 

 are in regard to the blue, the yellow and the 

 red. Sachs states, p. 696, that curvature takes 

 place behind a blue solution of ammoniacal 

 oxide of copper as in full daylight. This is 

 scarcely exact, because curvature is more 

 prominent behind the blue screen than be- 

 hind diffused daylight. It is also shown 

 clearly here that curvature does take place 

 behind red and behind yellow, though they 

 produce less of a phototropic stimulus than 

 any of the others, the yellow being stronger 

 than the red. Wiesner states that no curva- 



ture takes place behind yellow, though he 

 assigns some phototropic effect to red. An 

 extra series was arranged to test the point as 

 to whether no c"urvature takes place behind 

 yellow or red. Lateral illumination was 

 given through each of these two screens in 

 different lanterns, and it was found that both 

 produced distinct curvature. The lanterns 

 were arranged so as to admit diffused sky- 

 light and also, at other times, weak diffused 

 light from the room through the screens. In 

 every case there was the same result. 



Another series of experiments was per- 

 formed with these colored screens to deter- 

 mine the decoloring effect of such light upon 

 chlorophyll in solution. The solutions were 



fresh alcoholic solutions and in each test the 

 solutions were of exactly the same concentra- 

 tion, but solutions of different degrees of 

 concentration were used to see if strength 

 of solution had anything to do with the re- 

 sults. The conclusions reached were as sum- 

 marized in Fig. 2, /, and in the following order 

 commencing with the quality of light having 

 the greatest decoloring effect: 1, Diffused 

 light (in no case was direct sunlight used in 

 the test) ; 2, yellow; 3, blue; 4, red; 5, violet; 

 6, green; 7, darkness. The result of this ex- 

 periment showed that there was but small 

 relationship between the phototropic effects 

 ami the decoloring effects upon chloroiihyll in 

 so, 7»^n. It is quite clear that there is little 

 in CO. j)on (see Fig. 2, I and //). Sachs and 

 Wiesner both say that the rays of low re- 



