242 PIGMENTS 



CAROTIN C^H^. 



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 

 corona of the common Narcissus, N. Poeticus ; similarly the 

 presence of innumerable small intracellular crystals of carotin 

 are responsible for most of the colour of the root of the carrot, 

 and so also is the tint of many fruits where the carotin is often 

 in amorphous granules. 



With regard to the physiological significance of carotin, the 

 work of Tammes and Kohl * shows that carotin absorbs cer- 

 tain rays of radiant energy which can be made use of in photo- 

 synthesis. 



In addition to this there is the possibility that carotin may 

 be of importance in respiration, acting in a manner comparable 

 to the haemoglobin of the blood, f 



The possible function of the carotinoids in assimilation has 

 already been referred to on page 230. 



In those cases where a large amount of carotin occurs in 

 organs of storage, such as the roots of the carrot, it may be of 

 value as a reserve food-material. Finally, where the colours 

 of flowers are due to its presence, carotin is important in the 

 floral biology. 



Carotin is insoluble in water and very slightly soluble in 

 acetone or cold alcohol ; in hot alcohol it is more soluble ; 

 and in ether, chloroform, light petroleum, and carbon bi- 

 sulphide it is readily soluble. The colour of the solution 

 varies from yellow to red ; on crystallization flat reddish- 

 yellow plates are formed which exhibit the phenomenon of 

 dichroism, being orange-red by transmitted light and greenish- 

 blue in reflected light. 



According to Willstatter, \ carotin may be extracted from 

 stinging nettle leaves by light petroleum ; it has the mole- 

 cular formula C 40 H 56 , and is probably identical with the sub- 



* Kohl : " Ber. deut. hot. Gesells.," 1906, 24, 222. 



tArnaud: " Compt. rend.," 1889, 109, 911. 



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



