Chapter 7 

 Chlorophyll and the Chloroplasts 



1. Chlorophyll 



The green pigment of leaves has been the subject of scientific investi- 

 gation for a great many years. Even prior to the discovery of photo- 

 synthesis and before the importance of the green color for the develop- 

 ment of the plant was recognized, much study was devoted to the chem- 

 istry of the pigments of leaves, and several names which are famous in 

 the annals of chemistry, such as Berthollet, Proust and Berzelius are asso- 

 ciated with the early attempts to determine the nature of the leaf pig- 

 ment. With the realization of the significance of the green pigment to 

 virtually all life on the planet, the interest in this substance also grew 

 rapidly and it was soon regarded as one of the most important substances 

 in nature. That the large number of investigations of the nature of 

 the leaf pigments yielded relatively little valuable information must be 

 ascribed to the great instability of these compounds and to the fact that 

 chemical technique had not been sufficiently developed to enable workers 

 to handle these compounds. 



The suggestion of the term "chlorophyll" is usually ascribed to Pelle- 

 tier and Caventou ; ' these authors also finally recognized the fact that this 

 was not a single substance but a mixture of a number of compounds. We 

 cannot here go into a discussion of the development of the chemistry of 

 the leaf pigments; the subject has been adequately treated by others.^ 

 Most of the efforts have been directed toward establishing the chemical 

 composition and the constitution of the very complex molecules of the 

 chlorophyll pigments and to determine the physical properties of these, 

 especially in relation to the absorption of light. Relatively little work has 

 been done on the role which the chlorophyll pigments play in the photo- 

 synthetic process. 



^Pelletier and Caventou, Ann. Chiin. Phys. (2), 9, 194 (1818); (2), 51, 182 

 ( 1832) 



'Cz'apek, "Biochemie der Pflanzen.," 2 Ed., Jena, 1913, Vol. I, p. 555. Will- 

 statter and Stoll, "Untersuchungen iiber Chlorophyll," Berhn, 1913. Marchlewski, 

 "Chemie der Chlorophylle," Braunschweig, 1909. Tswett, "Chlorophylls in the 

 Plant and Animal Worlds" (Russian), Warsaw, 1910. Palmer, "Carotmoids and 

 Related Pigments," Chemical Catalog Co., N. Y., 1922. Tschirch, "Untersuchungen 

 uber das Chlorophyll," Berlin, 1884. 



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