Dr. Gardner on the Action of Light upon Vegetables. 3 



therefore be produced by any of these rays, or by their peculiar 

 combination. (See Sir J. F. W. Herschel's paper in the Philo- 

 sophical Transactions for 1840, p. 24, on " the combined action 

 of rays of different degrees of refrangibility.") 



(5.) I shall not attempt to explain the discrepancy between 

 my results and those of Mr. Hunt, for I do not esteem researches, 

 such as all the foregoing, made with colored media, of any value 

 in this branch of, vegetable physiology. It is well to remark, 

 however, that in treating of the germination of cress-seed behind, 

 the blue, green, yellow, and red media, he states " that the earth 

 continued damp under the green and blue fluids, whereas it rap- 

 idly dried under the yellow and red." (p. 271.) This difference 

 would by most persons have been considered sufficient to retard 

 or "destroy" ? germination. 



(6.) Other engagements in 1842 interfered with my design of 

 examining this question with the spectrum, and it was not until 

 July, 1843, that such arrangements were made as are necessary 

 to the prosecution of the subject. 



(7.) The apparatus. — A beam of the sun's light was directed 

 by a heliostat placed outside my window, along a square tube 

 of wood, passing through the shutter. The inner extremity of 

 the tube was closed, and contained near its end a flint glass equi- 

 lateral prism, one inch on the side and six inches long, with the 

 axis adjusted perpendicularly. The dispersed light passed into 

 the chamber, through an aperture in the side of the tube. All 

 that portion of the beam, which exceeded the breadth of the 

 prism, was cut off by a diaphragm. The object of these ar- 

 rangements was to render the room dark. The experiments 

 were performed in Virginia, in latitude 37° 1CKN., and continued 

 from July 6th to October 1st, during a season of unusual brill- 

 iancy and temperature. 



(8.) Arrangements for the experiments. — Seedlings of turnips, 

 radish, mustard, peas, several varieties of beans, peas, and the 

 following transplanted specimens, were used — Solarium nigrum, 

 S. Virginianum ; Plantago major, P. minor ; Polygonum hy- 

 dropiper ; Chenopodium rubrum ; Rumex obtusifolius. They 

 were placed in boxes with partitions, or planted in jars and grew 

 in darkness until ready for experiment, so that they acquired a 

 yellow color. The number of plants exposed to each ray aver- 

 aged one hundred, when the smaller seeds were used, and the 



