CAROTINOIDS 241 



alcoholic potash. When the green colour has returned dilute 

 with 10 c.c. water, added in portions, and add 'a little more 

 ether. On shaking, two layers separate ; the lower aqueous 

 alkaline layer contains the chlorophyll while the ether contains 

 carotinoids. 



5. To separate xanthophyll from carotin wash the ethereal 

 solution of these two substances obtained from previous 

 experiment with a little water and evaporate to i c.c. Dilute 

 with 10 c.c. of light petroleum, and shake up two or three 

 times with 10 c.c. of 90 per cent methyl alcohol until the 

 latter is no longer coloured. The methyl alcohol will con- 

 tain the xanthophyll while the carotin will be in the light 

 petroleum. 



THE CAROTINOIDS OR YELLOW PIGMENTS ACCOM- 

 PANYING CHLOROPHYLL. 



In addition to chlorophyll three 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, xanthophyll, and fuco- 

 xanthin. 



Of these pigments the most important are carotin and 

 xanthophyll, which were at one time supposed to be identical. 

 Thus Tammes* considers that most yellow pigments, whether 

 in separate plastids or associated with the chloroplasts, consist 

 of carotin. From the researches of Arnaudf and Willstatter 

 and Mieg:j: there is no doubt that xanthophyll and carotin are 

 different substances. 



Willstatter and Escher,§ moreover, have isolated from the 

 fruits of the tomato a yellow pigment, lycopin, isomeric with 

 carotin. It differs, ho^vever, from carotin in some of its 

 physical properties and in the amount of oxj^gen it takes up 

 on oxidation. 



Although carotin and xanthophyll are commonly associated 

 with chlorophyll they are not antecedents of this substance. 



* Tammes : " Flora," igoo, 87, 205. 

 + Arnaud : " Bull. Soc. Chim.," 1887, 48, 64. 

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

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

 16 



