REACTION OF PLANTS IN COLORS 315 



were excellent. He studied the reactions of white mus- 

 tard and cress seedlings in three different solar prismatic 

 spectra produced respectively by means of flint glass, 

 rock salt, and quartz. All diffuse light was eliminated by 

 means of suitable screens, and twenty-five different tests 

 were made. In all three spectra there were two regions 

 of maximum effect. The primary maximum lay in the 

 violet or ultra-violet in all cases, and the secondary maxi- 

 mum between the infra-red and the green. The minimum 

 effect in all cases was in the blue near the Fraunhofer 

 line F. 



These conclusions were in the main confirmed by the 

 thorough work of Wiesner (1879). Wiesner studied the 

 reactions of stems and roots of several different seedlings 

 behind thoroughly tested absorbing media and in differ- 

 ent parts of a direct sunlight spectrum produced by means 

 of the " Soleil'sche apparat mit Flintglasprisma." The 

 spectrum " showed the Fraunhofer lines clearly " and was 

 consequently relatively pure. I shall mention but one of 

 the numerous experiments the results of all of which agree 

 in general. In this experiment numerous pots of Vicia 

 sativa were distributed in the spectrum from infra-red to 

 ultra-violet. The seedlings between the violet and the ultra- 

 violet began to bend first, then those to the right and left, 

 and later those in the red. In the yellow and orange there 

 was no reaction. Wiesner states the results in the fol- 

 lowing words (1879, p. 190): " Schon nach ij Stunde 

 waren die an der Grenze zwischen Violett und Ultra- 

 violett (H-J) befindlichen Pflanzchen nach vorn genelgt. 

 Nach Ablauf von etwa f Stunde folgten die im mittleren 

 Violett und Ultraviolett aufgestellten; eine Viertelstunde 

 spater neigten sich die im Indigo stehenden, 10 Minuten 

 hierauf die im Blau, nach weiteren 20 Minuten die im 

 Griin und Ultraroth stehenden, sodann, nach einer Viertel- 

 stunde die im aussersten Roth, und nach einer weiteren 

 Viertelstunde die im Roth von B-C. Die Keimlinge in 

 Gelb und Orange standen jetzt, d. i. nach vollen 3 Stunden, 



