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ON THE INFLUENCE OF LIGHT ON SEEDS AND PLANTS. 75 



Researches on the Influence of Light on the Germination of Seeds 

 and the Growth of Plants. By Mr. Robert Hunt, Secretary to 

 the Royal Cornwall Polytechnic Society. 



The British Association having committed to my care this interesting in- 

 quiry, to which I had the satisfaction of first drawing attention, I feel it is 

 incumbent on me to furnish to the present meeting some account of the 

 results of my researches, as far as I have proceeded with them. I wish it 

 to be particularly understood, that this communication does not pretend to 

 contain anything, which can fairly be looked upon as pointing to any defi- 

 nite laws, or which can support any theoretical view of the influence of 

 solar light on vegetation. As it was not possible to commence my ob- 

 servations, in series, until January, the short time which has elapsed has not 

 permitted of my varying the conditions under which my experiments have 

 been tried. Had I been enabled to do so, I should in all probability have 

 had it in my power to explain with some approach to correctness, the causes 

 which have operated in the production of some of the effects described, but 

 on which I am scarcely enabled to speculate in the present state of the in- 

 quiry. I simply record the facts as they stand, trusting they will prove the 

 singular importance of the subject, which promises to lead us to a clear 

 view of many of the most mysterious functions of plants, to explain some of 

 the most interesting phasnomena of vegetable life, and beyond this, to deve- 

 lope properties in light which have not yet been discovered. 



Before I proceed to the principal subject of this paper, it is necessary I 

 should particularly describe the arrangements with which I have operated. 



Six boxes have been so prepared, that air was freely admitted to the plants 

 within them, without permitting the passage of any light, except that which 

 passed through the coloured glasses with which they were covered. 



These glasses permitted the permeation of the rays of light in the follow- 

 ing order. 



1. A Ruby Glass, coloured ivith Oxide of Gold This glass permits the 



permeation of the ordinary red, and the extreme red rays only. 



2. A Brown Red Glass. — The extreme red ray appears shortened ; the 

 ordinary red ray, and the orange ray pass freely, above which the spectrum 

 is sharply cut off. 



3. Orange Glass. — The spectrum is shortened by the cutting off of the 

 violet, indigo, and a considerable portion of the blue rays. The green ray is 

 nearly absorbed in the yellow, which is considerably elongated. The whole 

 of the least refrangible portion of the spectrum permeates this glass freely. 



4. Yellow Glass, somewhat Opalescent. — This glass shortens the spec- 

 trum by cutting off the extreme red ray, and the whole of the most refran- 

 gible rays beyond the blue ray. 



5. Cobalt Blue Glass. — The spectrum obtained under this glass is 

 perfect from the extreme limits of the most refrangible rays down to the 

 yellow, which is wanting. The green ray is diminished, forming merely a 

 well-defined line between the blue and the yellow rays. The orange and 

 red rays are partially interrupted. 



6. Deep Green Glass. — The spectrum is cut off below the orange and 

 above the blue rays. Although the space on which the most luminous por- 

 tion of the spectrum falls appears as large as when it is not subjected to the 

 absorptive influence of the glass, there is a great deficiency of light, and on 

 close examination with a powerful lens, a dark line is seen to occupy the 

 space usually marked by the green ray. 



A case has also been prepared containing five flat vessels filled with dif- 



