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



panying it, there is an action from +10.5 to +36.0 of the same 

 scale, beginning abruptly in Fraunhofer's blue. So striking 

 is this whole result, that some of the earlier spectra obtained by 

 me, contained a perfectly neutral space from —5.0 to +10.5, in 

 which the chlorophyl was in no way changed, whilst the solar 

 picture in the red was sharp and of a dazzling whiteness, and the 

 maximum of the indigo was also bleached — producing a linear 

 spectrum, as in fig. 2, in which the orange, yellow and green 

 rays are inactive ; these it will be remembered are energetic in 

 forming the green matter. 



Fig. 2. ^ m ^^ mminamM 

 Red, orange, yellow, green, blue, indigo, violet. 



Upon longer exposure, the subordinate action along the yellow, 

 &c. occurs, but not until the other portions are perfectly bleached. 



In Sir J. Herschel's experiments there remained a salmon 

 color, after the discharge of the green. This is not seen when 

 chlorophyl is used, and is due to a coloring matter, insoluble in 

 ether. 



(40.) No ground exists therefore for the theory that the au- 

 tumnal tint of leaves is due to the residual, after the destruction 

 of the green color. Xanthophyl, which imparts the yellow, de- 

 pends on an organic change of chlorophyl, which Berzelius could 

 not imitate. (Journ. de Pharm. Juillet, 1837.) 



Some observations made with a view of determining the action 

 of indigo light on the green of living plants, brought me to the 

 conclusion, that it faded into a yellowish green color — but I will 

 not speak positively. Plants do, however, lose all their green- 

 ness in a dark place, after a greater or less time, and become of 

 the color of seedlings raised without light. In this result my 

 experience is at variance with the statement of Macaire Princep, 

 "Les feuilles d'une plante conservees a l'abri de la lumiere s'en 

 detachent colorees vert." (In Berzelius, Chimie, t. 6, p. 42; 

 from Mem. de la Soc. Hist. Nat. de Geneve, t. 4.) 



(41.) In the bleaching of chlorophyl, as well as in its produc- 

 tion, the active agent is light, for it will take place behind a me- 

 dium excluding the tithonic rays, and the points of activity have 

 no relation to the maxima of the calorific spectrum. See Sir John 

 Herschel's paper, (Phil. Trans. 1840, Part I, p. 51,) "on the dis- 

 tribution of the calorific rays of the solar spectrum." 



