4 6 4 



THE QUARTERLY REVIEW OF BIOLOGY 



or slightly modified, are the cause of the 

 yellow to red chromolipoid colors of all 

 species of animals. 



FUNCTION OF THE CAROTINOIDS 



This review of the carotinoid pigments 

 would not be complete without discussing 

 briefly their function in living organisms. 

 Many views have been held regarding 

 these pigments. 



IN PLANTS 



Engelmann (1887) and Kohl believed 

 that carotin shares with chlorophyll the 

 work of carbon dioxide assimilation and 

 that this lies chiefly in its energetic absorp- 

 tion of a large part of the blue violet rays 

 of sunlight. The spectroscopic properties 

 of the carotinoids are one of the strongest 

 arguments in favor of the view that they 

 perform some definite function in the 

 plant. Went C1904) thinks that they may 

 serve the purpose of protecting the cell 

 enzymes against the destructive action of 

 certain light rays. Kohl (1900) and 

 Arnaud have suggested that carotin may 

 act in a respiratory role through its power 

 to absorb oxygen. Willstatter and Stoll 

 suppose that carbon dioxide assimilation is 

 controlled by an equilibrium between the 

 chlorophyll components a and b and that 

 this equilibrium is in turn controlled by 

 the carotinoids. Willstatter and Mieg on 

 the other hand thought that carotinoids 

 might help regulate the oxygen pressure in 

 plant cells through their great affinity for 

 this element. Ewart (191 5) has attempted 

 to show that carotin and xanthophyll can 

 play a part in photosynthesis. His work, 

 however, has been seriously questioned. 

 Up to the present time very little study 

 has been made of the physiological condi- 

 tions which govern the formation of the 

 carotinoids in plants or to the problem of 

 the relations between the different caro- 



tinoids or between the carotinoids and the 

 other plant constituents. In ripening 

 tomatoes, carotin and lycopin formation is 

 coincident with the destruction of chloro- 

 phyll, but there is no chemical basis for 

 assuming that this indicates that the 

 carotinoids are actually derived from 

 chlorophyll. Duggar (1913) has found 

 that the formation of the carotinoids in 

 ripening tomatoes may be correlated with 

 temperature. The synthesis of lycopin he 

 found was independent of light but was 

 dependent upon oxygen. In cases of 

 oxygen exclusion the fruit failed to redden, 

 even at a favorable temperature. 



IN ANIMALS 



In the case of animals all of the evidence 

 presentable argues against the carotinoids 

 performing any general physiological func- 

 tion. Attempts have been and are still 

 being made to correlate the carotinoids 

 with the vitamines but as yet no success 

 has been obtained. There appears, how- ■ 

 ever, to be a fairly definite correlation j 

 between the occurrence of carotinoids and ; 

 vitamine A in plant tissues but not in 

 animal tissues or in animal fats. 



In the above discussion the writer has | 

 attempted to review the present state of : 

 our knowledge of the carotinoid pigments. 

 An effort has also been made to indicate : 

 the long slow evolution of our knowledge I 

 of these pigments and to show that much 

 effort has been put forth by a great many ( 

 workers to establish our present concep-i 

 tions regarding the chemical nature and; 

 the number of the carotinoid pigments. 

 Perhaps at the present time information 1 

 regarding the complex chemical structure 

 of the pigments will do much to solve 

 many of the perplexing problems. Until 

 the chemical structure of these pigments is 

 fully- worked out there will probably be 

 much speculation regarding their real 

 nature in plant economy. 



