PLANT PIGMENTS 



Their color and interrelationships 

 B. HOROWITZ 



Introduction. In attempts to explain the action of ammonia 

 on thymol,^ Prof. Gies and the author were led to review the work 

 of Liebermann on the influence of ammonia upon orcinol.^ Lieber- 

 mann's Suggestion that ammonia combines with oxygen of the air 

 to form nitrous acid, and that the latter is the effective agent in the 

 production of pigment, strengthened our view, as already held, that 

 many plant pigments are synthesized in a similar way. Miss Wake- 

 man's study of the pigments in the Monardas,^ whereby she came 

 to the conclusion that these are probably oxidation products of 

 thymol, and its isomer, carvacrol, and Wurster's suggestive paper 

 on the role of hydrogen peroxid in color formation,^ afforded fur- 

 ther evidence in support of this idea. During the past year the 

 thymol problem has been studied side by side with an investigation 

 into the chemistry of some plant pigments (the botanical side of 

 which is engaging the attention of Dr. A. B. Stout, of the N. Y..' 

 Botanical Garden). As an introduction to a description of these 

 studies, we present herewith a brief review of the theories on color 

 and chemical Constitution, as well as an outline of the possible 

 chemical interrelationships of some of the more important plant 

 pigments. 



Color and chemical Constitution. Perhaps one of the most 

 fascinating chapters in the development of organic chemistry has 

 been the attempt to correlate the chemical Constitution of substances 

 with their physical properties. With the rise of synthetic chem- 

 istry, and especially as a result of the pioneer work of Graebe, 

 Liebermann and Baeyer in the production of synthetic dyes, color 



^Gies: Biochem. Bull., 1912, ii, p. 171. Horowitz and Gies: Ibid., 1913, ii, 

 p. 293. Horowitz : Dissertation, Columbia Univ., 1913, pp. 68. 



2 Liebermann : Ber. d. d. ehem. Gesell., 1874, vii, p. 247. 



3 Wakeman : Bulletin of the Univ. of Wisconsin, No. 448; Science series, 

 191 1, iv, p. 25. 



* Wurster : Ber. d. d. ehem. Gesell., 1887, xx, p. 2934. 



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