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On the Action of Yellow Light in producing the Green Colour, 

 and Indigo Light the Movements of Plants. By D. P. 

 Gardner, M.D., Cor. Memb. Lye. Nat. Hist. New York. 



1. The object of this paper is to prove the existence of dif- 

 ferent properties in the rays of the spectrum, in their action 

 on vegetables ; and more especially to shew that the rays 

 which produce the green colour of plants, are altogether dis- 

 similar from those which influence their movements towards 

 light, the colour being developed by the less refrangible rays, 

 and chiefly by the yellow ; whereas, the motion is influenced 

 by indigo light. The discussion of the subject will be divided 

 under three heads : 



1. On the production of chlorophyl by yellow light. 



2. On the movements of plants towards indigo light. 



3. Some application of these facts to vegetable physiology, 



1. On the production of chlorophyl by yellow light. 



(2.) It is a fundamental fact in botany, that light is neces- 

 sary to the formation of chlorophyl. Von Humboldt adduced 

 certain exceptions to this law, in the case of plants found in 

 the mines of Freyberg, and, with Senebier, ascribed the green 

 matter to the action of hydrogen gas. But the experiments of 

 the latter failed in the hands of De Candolle, and a series in- 

 stituted by myself, and conducted with great care, were equal- 

 ly unsuccessful. On the other hand, Humboldt succeeded in 

 greening a plant of Lepidimn sativum^ raised in darkness, by 

 the light of two lamps, and De Candolle obtained the same 

 result with six Argand lamps. 



(3.) The investigation has been subsequently confined to 

 the name of the ray which produces chlorophyl.* Formerly 



* Chlorophylj the green matter of leaves. It is insoluble in water, 

 but soluble in ether and alcohol. The ultimate analysis has not been 

 made ; but chemists agree that it is of the nature of wax. The yellow 

 colour of autumnal foliage is due to a similar yellow wax, called Xan- 

 thopliyl, supposed to be produced by the action of frost on the former 

 substance. 



