88 Dr Gardner on the Action of Light on Vegetables, 



the first case of a movement^ perceptible to the eye, being 

 traced to the unaided action of light. That this unponderable 

 produced molecular changes, was readily admitted ; but its in- 

 fluence, in bringing about palpable movements of considerable 

 extent, has never been suspected. In the irritability of the 

 iris, physiologists have always seen the influence of nervous 

 matter ; but in plants no such agent exists to complicate the 

 phenomenon ; and, therefore, the action is due to light only. 



In this newly discovered property light is also more closely 

 assimilated to the other unponderables ; for both heat and 

 electricity are capable of producing palpable motion. 



3. Some applications of the preceding facts, Sfc. 



(35.) Numerous applications to vegetable physiology will 

 suggest themselves to the reader ; but it is my purpose to treat 

 only of the following : 



The intimate relation which exists between the rags which 

 produce chlorophgl, the decomposition of carbonic acid, and the 

 luminous spectrum. The maximum for the formation of green 

 matter has been shewn to reside in the yellow ray. Dr 

 Draper (Lond. and Edin. Phil. Mag., Sept. 1843) discovered 

 the maximum action, for the decomposition of carbonic acid, 

 to be between the green and yellow ; or, more correctly, in the 

 centre of the yellow. Sir W. Herschel and Fraunhofer 

 placed the maximum for light in the same space. 



(36.) The relation goes further ; for if the quantities obtain- 

 ed by Dr Draper for decomposing action, as measured by 

 liberated gas — Fraunhofer, for illuminating power, determined 

 i>y the eye — ^and my estimate, obtained in time, and by the 

 eye — be rendered commensurable and tabulated, they will 

 give quantities nearly allied. To produce such a table, I 

 assume all the maxima equal to unity. My results being in 

 time, and theirs in efilsct, the inverse proportion is taken for 

 each value given in Art. 14. 



