266 CAROTINOIDS AND RELATED PIGMENTS 



point in favor of their independent existence, but does not, of course, 

 show that the chlorophylls and carotinoids do not arise from a com- 

 mon nucleus. From a chemical point of view the most likely sub- 

 stance which could thus give rise to both carotinoids and chlorophyll 

 would be isoprene, C 5 H 8 , the terpene "baustein" which may go to 

 phytol on the one hand, as Willstatter believes, and perhaps could also 

 go to carotin on the other. 



Very little study has been given to the physiological conditions which 

 govern the formation of the carotinoids in plants or to the problem of 

 the relations between the different carotinoids or between the caroti- 

 noids and other plant constituents. The Toblcrs (1912) observed that 

 the carotin content of carrots increased during the formation of starch 

 from sugar, but it is difficult to decide from this observation that the 

 carotin plays any part in the process. These investigators (1910b, 

 1912) have also shown that the formation of carotin and lycopin in the 

 ripening of tomato fruits is coincident with the destruction of chloro- 

 phyll. Lubimenko (1914a) has concluded that the lycopin forms in 

 this case at the expense of the chlorophyll, but there is no chemical 

 basis for assuming that this indicates that the carotinoids are actually 

 formed from the chlorophyll. 



Duggar (1913) made an especially interesting study of the develop- 

 ment of carotinoids in tomato fruits. He found that the factor for 

 carotin formation and the factor for lycopersicin (lycopin) formation 

 are present together in the fruits which normally redden on ripening, 

 but that the formation of the red carotinoid could be partially or com- 

 pletely suppressed by ripening the green fruits at a temperature of 

 30 C. or above. At these temperatures the fruits ripened with a yel- 

 low color and contained only carotin and xanthophylls. The inhibition 

 of the lycopin was found to be proportional to the temperature (be- 

 tween 30 and 37 C.), but was inversely related to the age of the 

 fruits, the oldest fruits requiring a higher temperature for the sup- 

 pression of reddening. The failure of the fruits to develop lycopersicin 

 at the higher temperatures was found to be a true suppression, inas- 

 much as the red pigment formed rapidly when the yellow fruits were 

 returned to a lower temperature. Duggar was also able to show very 

 satisfactorily both by means of the microscope and the spectroscope 

 that the lycopin which formed in these cases could not have been de- 

 rived from the carotin present. 



Duggar also made a study of other factors entering into the forma- 

 tion of the lycopin of tomatoes, with the result that the synthesis of 



