REACTION OF PLANTS IN COLORS 319 



150 ca. m. seconds), neutral in strong light (100,000- 

 200,000 ca. m. sec.)/ and negative in very strong light 

 (2,000,000-12,000,000 ca. m. sec). However, the red and 

 yellow rays are, under all conditions, relatively more effi- 

 cient in the molds than in green plants. The difference 

 in the distribution in the spectrum of the stimulating 

 efficiency in different intensities of light may possibly 

 account for the discrepancies in the results of former 

 investigation in this field. 



Summary 



(i) According to Gardner all visible rays are active in 

 producing curvature in plants; according to Dutrochet 

 and Pouillet, Guillemin and Miiller, plants respond to all 

 visible rays and some ultra-violet and infra-red as well; 

 according to Wiesner they respond to all rays in the visi- 

 ble spectrum except some yellow and orange, and possibly 

 some beyond at either end; according to Kraus and Bre- 

 feld the red is nearly as active as the blue in causing 

 reactions in the molds; according to Blaauw all the visible 

 rays of the spectrum and some ultra-violet produce cur- 

 vature in oats seedlings and molds, but the longer waves 

 are relatively more active in the latter than in the former; 

 according to Sachs and Payer only the shorter waves are 

 active. Thus it is seen that all but Sachs and Payer 

 obtained reactions to the longer as well as to the shorter 

 waves of the spectrum, and since nearly all of these inves- 

 tigators used relatively pure prismatic colors and efficient 

 methods in other respects, it is evident that the great bulk 

 of evidence goes against Sachs' conclusion that only the 

 shorter waves are active in light reactions in plants. 



(2) The experimental results of all the investigators 



^ " Candle-meter seconds " indicates the product of the time of exposure 

 and the intensity of the light. This, Blaauw maintains, is a constant for 

 the threshold of a given plant, that is, the higher the intensity, the shorter 

 the time of exposure required to produce a reaction. 



