374 PHOTOSYNTHESIS 



that the Hmits of the absorption bands undergo a change after illumina- 

 tion, following fertilization with certain mineral salts and with age. He 

 considers that this displacement of the absorption bands is due to a change 

 in the proportion of the two chlorophyll components and believes to have 

 found evidence for the theory that the ratio of the two components 

 alters during photosynthesis. It is a question, however, whether the 

 observed displacements of the absorption bands cannot be ascribed to a 

 number of other causes as well. 



It will be remembered that Baeyer, in formulating the theory that 

 formaldehyde is an intermediate product in the photosynthesis of carbo- 

 hydrates, assumed that the function of chlorophyll was to combine with 

 carbon monoxide, which had been formed by the action of light on car- 

 bon dioxide. He thus assumed that chlorophyll had properties similar 

 to hemoglobin in its power to combine with carbon monoxide and that 

 the latter was then reduced to formaldehyde. This was probably the 

 first time that it was suggested that chlorophyll may enter directly into 

 the chemical reactions of photosynthesis. Various modifications of this 

 idea have appeared from time to time. Hoppe-Seyler '^^ considered the 

 possibility of a loose union of chlorophyll and carbon dioxide in which 

 condition the latter was reduced and subsequently chlorophyll liberated 

 again. 



Willstatter and Stoll '- have developed a theory of the function of 

 chlorophyll based upon their studies of the action of carbon dioxide on 

 chlorophyll. When solutions of chlorophyll in organic solvents, such as 

 ether, are treated with carbon dioxide, there is no evidence of chemical 

 reaction. There is no difference in the absorption of carbon dioxide 

 between pure alcohol and an alcoholic solution of chlorophyll. On the 

 other hand, colloidal solutions of chlorophyll in water, show an absorp- 

 tion of carbon dioxide and chemical reaction occurs. The final evidence 

 of this reaction is the splitting out of magnesium from the chloro- 

 phyll, as occurs with other acids, with the formation of phneophytin : 

 C55Hv205N4Mg -f COo + H.O > AIgC03 + C^.'^.^O^'K^. On com- 

 paring the solubility of carbon dioxide in water and in colloidal chloro- 

 phyll solutions, it was found that the latter was considerably higher. In 

 similar experiments carried out by Kremann and Schniderschitsch '^ no 

 absorption by chlorophyll could be observed. This, Willstatter and Stoll 

 maintain, was due to the use of impure preparations in which the chloro- 

 phyll had been precipitated. 



The reaction of chlorophyll with carbonic acid is complete when the 

 chlorophyll has been entirely decomposed according to the equation just 

 given. However, Willstatter and Stoll are of the opinion that in this 

 reaction an intermediate product is formed, a compound of chlorophyll 

 and carbonic acid. This intermediate product is dissociable and is capable 



"Hoppe-Seyler, "Physiologische Chemie," Berlin, 1881. 

 "WillstiiUer and Stoll, "Untersuch. li. Ass. der Kohlensiiure," p. 226. 

 "Kremann and Schniderschitsch, Momtsh., 37, 659 (1916). 



