154 Plant Pigments [March, 



Carotin is of interest because of its probable physiological sig- 

 nificance. The work of Tammes^ and Kohl^° shows that Carotin 

 absorbs certain rays of radiant energy, which can be made use of in 

 photosynthesis. It may also be of importance in respiration, acting 

 in a manner comparable to the hemoglobin of the blood. Palladin^^ 

 supposes that, by the action of an oxidase, Carotin is changed into 

 xanthophyll (C40H56O2), which in turn is acted upon by a reduc- 

 tase, yielding Carotin. In cases where large amounts of Carotin 

 occur in organs of storage, such as the roots of the carrot, it may 

 be of value as a reserve food material. Finally, where the colors of 

 flowers are due to its presence, it is of importance in floral biology. 



Experiments by Iwanowski/ ^^ in which Chlorophyll Solutions 

 containing various amounts of yellow pigments ( Carotin and xan- 

 thophyll) were subjected to the action of sunlight, show that with 

 the increase of the relative content of yellow pigments the stability 

 of the Chlorophyll towards light also increased. While this protec- 

 tive action is exercised by both Carotin and xanthophyll individually, 

 a more favorable effect is obtained by a mixture of the two. This 

 action is probably due to the absorption of the blue and, especially, 

 the violet rays, whose chlorophyll-destroying power is very high. 

 It is not yet established whether the oxygen absorption of these pig- 

 ments plays a röle in this process. 



Mention may be made here of the recent studies of Palmer and 

 Eckles^^ on Carotin and xanthophyll. They have shown that the 

 fat of cow milk owes its natural yellow color to the presence of Caro- 

 tin and xanthophyll (principally Carotin), which are taken up from 

 the food and subsequently secreted in the milk fat. The same pig- 

 ments are found in the body fat, blood serum, corpus luteum, and 

 human milk. Carotin is assimilated from the food of the cow in pref- 

 erence to xanthophyll, partly because of its greater stability toward 

 the digestive Juices.^ ^ It probably forms by far the greater part 



9 Tammes : Flora, 87, 205, 1900. 



10 Kohl : Ber. d. deutsch, bot. Gesellsch., 24, 222, 1906. 

 iiPalladin: Ibid., 26a, 125, 378, 389, 1908; 27, iio, 1909. 

 "a Iwanowski : Ibid., 31, 600, 613, 1913-1914. 



12 Palmer and Eckles : Jour. Biol. Chem., 17, 191. 211, 223, 237, 245, 1914; 

 Research Bulletin, No. 10, Missouri Exper. Station. 



13 Cf. Willstätter and Mieg (2), who State that xanthophyll is very sensitive 

 to acids. 



