CAROTINOIDS 239 



THE CAROTINOIDS OR YELLOW PIGMENTS ACCOM- 

 PANYING CHLOROPHYLL. 



In addition to chlorophyll four pigments which are in- 

 ^soluble in the cell sap occur in plants either in a relatively 

 pure form in chromoplasts, or associated with chlorophyll in 

 the chloroplasts ; they are carotin, lycopin, xanthophyll, and 

 fucoxanthin. Of the carotinoids, the most important are 

 carotin and xanthophyll, which were at one time supposed to 

 be identical. From the researches of Arnaud * and Willstatter 

 and Miegf there is no doubt that xanthophyll and carotin 

 are different substances. Willstatter and Escher,J moreover, 

 have isolated from the fruits of the tomato a yellow pigment, 

 lycopin, isomeric with carotin. It differs, however, from 

 carotin in some of its physical properties and in the amount 

 of oxygen it takes up on oxidation. While according to some 

 authors the carotinoids have their origin in a particular kind 

 of elongated mitochondrium, they are, according to other 

 workers, to be regarded as decomposition products of chloro- 

 phyll. 



The colour changes in fruits and leaves are, according 

 to LubimenkoJI due to two classes of compounds which he 

 terms lycopinoids and rhodoxanthinoids, each of which may 

 be further subdivided according to their chemical and physical 

 properties. The lycopinoids may be either amorphous or 

 crystalline, and several may be associated in one chromo- 

 leucite ; during fruit ripening the amorphous lycopinoids 

 gradually change into the crystalline lycopin. The lycopin- 

 oids are more widely distributed than are the rhodoxanthoids ; 

 temperature is an important factor in their formation and 

 oxygen is an essential. 



* Arnaud: "Bull. Soc. Chem.," 1887, 48, 64. 

 f Willstatter and Mieg: " Annalen," 1907, 355, i. 

 Willstatter and Escher : "Zeit. physiol. Chem.," 1910, 64, 47. 

 Guilliermond : " Compt. rend.," 1917, 164, 232, 407, 609, 643; Mottier : 

 "Ann. Bot.," 1918, 32, igi. 



|| Lubimenko : "Compt. rend.," 1914, 158, 510. 



