Accompanying chlorophyll are three yellow or reddish- 

 brown pigments, Carotin, Xanthophyll, and Fucoxanthin (the 

 latter occurring only in brown algae), which are known col- 

 lectively as the Carotinoids. Owing to the similarity in 

 solubilities between these substances and chlorophyll, their 

 complete separation is a matter of some difficulty; it was 

 first effected by Willstatter and Hug.* 



The average proportions in which these various constituents 

 occur in different plants have been determined by Willstatter, 

 and are approximately as follows : 



From these figures the following interesting deductions 

 may be made : 



1. The molecular proportions between chlorophylls and 

 carotinoids are as 3-5 to I J in terrestrial plants, but only I to I 

 in the case of algae. 



2. In the brown algae chlorophyll a predominates, only 

 about 5 per cent of the mixture being chlorophyll b ; in ter- 

 restrial plants, on the other hand, the proportion is pretty 

 constantly about 3:1. 



3. In the green algae there is relatively more of chloro- 

 phyll b. 



Concerning the physiological significance of these sub- 

 stances it has been suggested by Willstatter S that since 



oo J O 



chlorophyll b (C 55 H 70 O 6 N 4 Mg) contains more oxygen than 

 chlorophyll a (C 55 H 72 O 5 N 4 Mg), the former compound is pro- 

 duced by the action of chlorophyll a upon carbon dioxide 



* Willstatter and Hug: " Annalen," 1911, 380, 177. 



f These figures are percentages calculated on the dry material. 



J With regard to this ratio, it has been stated by Willstatter that it is" re- 

 markably constant, and that there is a greater variation between different leaves 

 of the same plant than between corresponding leaves of different plants. This 

 view is, however, contested by Borowska and Marchlewski (" Biochem. Zeitschr.," 

 1913, 57, 423), who hold that it is entirely dependent on external circumstances, 

 such as soil, stage of growth, etc. 



Willstatter : " Untersuchungen uber Chlorophyll," p. 237. 



