REACTION OF PLANTS IN COLORS 317 



neutral, but that it actually causes a retardation in reac- 

 tion when mixed with other active rays. 



Miiller (1872) obtained varying results in his study of 

 the reactions of seedlings in the solar prismatic spectrum. 

 He found the region of maximum effect for cress to be in 

 the blue at line F, and that for Sinapis alba in the yellow 

 and upper part of the green between lines D and E. He 

 claims that this difference is due to the difference of absorp- 

 tion of light under different conditions and in different 

 plants. The farther a plant is from the prism the farther 

 the maximum extends toward the red end of the spectrum. 

 It may even extend into the infra-red. In case of cress 

 seedlings, e.g., set in a row extending from the prism, it 

 was found that those farthest away were neutral in violet 

 and blue but still reacted in green and yellow, whereas 

 those nearer the prism responded most strongly in the 

 violet and blue. Miiller thinks this is due to difference in 

 absorption of different rays under different conditions. 



The work of Sachs in 1864 and later, as already stated, 

 led to conclusions similar to those of Payer. Sachs 

 studied the reactions of various seedlings under double- 

 walled bell jars, some of which were filled with ammoniacal 

 solution of copper hydrate and others with potassium 

 bichromate. The former transmitted violet to green in- 

 clusive, the latter yellow to red. The seedlings under 

 the copper solution curved strongly, while those under 

 the chromate remained straight. Similar results were ob- 

 tained behind cobalt and ruby glass. These results are 

 not in accord with those of Guillemin, Wiesner and others, 

 who found that seedlings responded in the longer wave 

 lengths. The fact that Sachs could get no reaction in red 

 produced by sunlight passed through a solution of potas- 

 sium bichromate was probably, as Pfeffer points out 

 (p. 176), " the result of feeble intensity of the light used, 

 or of the special properties of the experimental material." 

 The experiments of Kraus (1876) with colored screens 

 show that the stalks of the perithecial heads of the fungus 



