FUNCTION OF CAROTINOIDS IN PLANTS, ANIMALS 263 



their own lipochromes, the fact that animals merely derive their lipo- 

 chromes preformed from their food does not invalidate the idea that 

 these pigments are merely casual products in the animal organism and 

 even suu^e-ts that they perform no useful purpose in the plants which 

 synthesi/e them. 



Possible Function in Plants 



Various theories have been advanced to explain the significance of 

 the earotinoids in plants. When Arnaud (1885) discovered the pres- 

 ence of carotin in green leaves he raised the question as to its possible 

 relation to chlorophyll and later (1889) suggested that the pigment 

 might play a role in plants similar to that of the hemoglobin of the 

 blood. He also attached considerable significance to the fact that 

 carotin, with its great affinity for oxygen when released from the living 

 plant tissues, remains apparently unaltered at an almost constant level 

 when in the living leaf. Arnaud could not explain this except on the 

 basis that the carotin was constantly undergoing an alternating oxida- 

 tion and reduction analogous to that of hemoglobin in the blood. 



Zopf looked upon the lipochromes as reserve products, but Miss New- 

 bigin (1898) has aptly stated that it is safer to admit merely that they 

 often occur in association with reserves. Zopf, however, apparently 

 limited his conception of carotin as a reserve substance to certain fungi, 

 such as the Uridinece (rusts) and certain molds. The idea was based 

 upon his observation that the pigment seems to concentrate in the 

 spores of these plants and later to disappear during germination. 

 Kohl (1902J) accepted this idea and in addition stated that he believed 

 that carotin acted as a reserve substance in the carrot root. 



Kohl has, in fact, given us the most comprehensive conception of the 

 various roles which carotin may play in plant life. Primarily he be- 

 lieves with Engelmann (1887) that carotin shares with chlorophyll 

 the work of carbon dioxide assimilation, and that this lies chiefly in 

 its energetic absorption of a large part of the blue-violet rays of sun- 

 light. This light is transformed into heat, a property which Staid 

 (1896) believed anthocyanin and carotin shared, permitting the pig- 

 ment to act indirectly as a catalyst for various metabolic processes, 

 including the decomposition of the atmospheric carbon dioxide. There 

 can be no doubt that the spectroscopic properties of the earotinoids are 

 one of the strongest arguments in favor of the view that they perform 

 some definite function in the plant. Whether the light absorbed is 

 transformed as Kohl believes or whether it serves some other purpose 



