USE OF THE SPECTROSCOPE IN STUDY OF PLANT LIFE. 97 



result of the direct action of the more refrangible half of the spectrum; 

 for Sachs' experiments with solutions of potassium bichromate, which 

 allows the red, orange, yellow, and part of the green rays to pass, 

 showed no heliotropic action to take place. But, if light passes through 

 a solution of ammoniacal oxide of copper, which is dark blue, and 

 allows violet and ultra-violet to pass, then heliotropic movements occur. 

 The same results followed the use of cobalt-blue sheet-glass, and ruby- 

 red instead of the orange-coloured potassium chromate. 



Sachs, however, mentions that others have obtained different results, 

 finding maxima in infra-red and ultra-violet rays.''' 



* Sachs'' Veyctabh P/iysiolo'ji/, p. 696. 



VOL. XXXVI. 



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