236 PIGMENTS 



phyll and haemoglobin, the following skeletons, involving the 

 assumption of subsidiary valencies, according to Werner and 

 others, have been suggested * : — 



-g>N. 'N<9- ~c>^\ .'N<g- 



Zg>N / ^- N<g- -g>N / I, ^ N<C- 



Chlorophyll H^ematin 



THE YELLOW PIGMENTS ACCOMPANYINCi 

 CHLOROPHYLL. 



In addition to chlorophyll several 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. 



Of these pigments the most important are carotin and 

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

 Thus Tammesf considers that most yellow pigments, whether 

 in separate plastids or associated with the chloroplasts, consist 

 of carotin. From the researches of ArnaudJ and Willstatter 

 and Mieg § 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, however, from carotin in some of its 

 physical properties and in the amount of oxygen it takes up 

 on oxidation. 



Although carotin and xanthophyll are frequently associated 

 with chlorophyll they are not antecedents of this substance. 



CAROTIN. 

 This pigment is widely distributed and, as has already been 

 mentioned, is generally associated with chlorophyll in the 

 chloroplasts. It also occurs in various forms, amorphous or 

 crystalline, in various parts of many plants. The colour of 

 yellow or orange petals is not infrequently due to it, e.g. the 



* Willstatter and Fritzsche : id., 1909, 371, 33. 



+ Tammes: "Flora," 1900, 87, 205, 



J Arnaud: " Bull. Sec. Chim.," 1887, 48, 64. 



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



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



