350 PHOTOSYNTHESIS 



the absorption spectrum shifts toward the red end of the spectrum. He 

 considers that the absorption spectrum cannot give a definite answer 

 regarding the state of the chlorophyll in the leaf. The proof of the 

 colloidal state of the chlorophyll in the leaf is rather to be sought in 

 the behavior of the pigments toward solvents. 



Herlitzka,^° apparently unfamiliar with Iwanowski's first publication, 

 concludes that the similarity of the spectra of living leaves and colloidal 

 chlorophyll solutions can be taken as evidence of the colloidal state of 

 chlorophyll in the leaf ; that the two, if not identical, are at least in a 

 similar state. Willstatter and Stoll also compared the absorption spectra 

 of leaves and of chlorophyll solutions. They found that the absorption 

 bands of living leaves and of colloidal chlorophyll solutions were identical, 

 although the intensity relations of the two were different. On the basis 

 of these observations and because of the behavior of the chlorophyll in 

 leaves toward solvents, they conclude that in the leaf the chlorophyll is 

 in a colloidal state. The fact has already been mentioned that pure 

 dry solvents as acetone, ether, benzol do not extract chlorophyll from 

 dried leaves. On the addition of water these solvents immediately take 

 up the chlorophyll. It is assumed that the water dissolves some of 

 the salts in the dried leaves, that this salt solution precipitates some of 

 the chlorophyll, and it should also be pointed out, that a colloidal solu- 

 tion of chlorophyll cannot be extracted with dry ether unless there is 

 present a small amount of calcium chloride. 



When leaves are put into boiling water for a short time the chloro- 

 plasts are ruptured, the chlorophyll diffuses out and the color of the leaves 

 changes to a deeper green. This change of color is associated with a 

 shifting of the spectral absorption bands toward the violet, and they are 

 very close to the position of the absorption bands of a true chlorophyll 

 solution. This Willstatter and Stoll interpret to mean that, due to the 

 action of the hot water, the chlorophyll has passed from a colloidal solu- 

 tion to a true solution. With this conception, that the chlorophyll in the 

 leaf is in a colloidal condition, the views of Stern, based upon his studies 

 of fluorescence, are at variance. The reasons for this conclusion are 

 given below. 



The fluorescence of chlorophyll is one of its most striking properties 

 and is especially noticeable in solutions of organic solvents. Brewster, 

 as early as 1834, observed this, and through the studies of Stokes ^^ the 

 nature of the phenomenon, as well as the very important fact, that chloro- 

 phyll in the living leaf is also fluorescent, were discovered. Spectrometric 

 determinations of the fluorescent light from solutions and living plants 

 were made by Hagenbach ^^ and by others, who used his method. This 

 consists in projecting a beam of white light, filtered through a blue solu- 



^Herlitzka, Biochem. Zcit., 38, 321 (1912). 



" Stokes, Phil. Trans. Roy. Soc, 1852, 463. Reinke, Ber. hot. Ges., 2, 265 (1884). 

 Simmler, Poqq. Ann. Phys., 115, 603 (1862). 



'^ Hagenbach, Pogg. Ann. Phys., 141, 245 (1870) ; Jubclb., 303 (1874). Lommel, 

 ibid., 143, 568 (1871). 



