314 PIGMENTS 



2. In the brown algae chlorophyll a predominates, only 

 about 5 per cent of the mixture being chlorophyll h ; 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. 



Other values have been obtained by Lubimenko * : — 



Amount of Chlorophyll. 

 0*46 per cent, of wet weight. 



That the amount of chlorophyll in the algae is not connected 

 with the depth of immersion is indicated by the values ob- 

 tained for Phyllophora ; further, Laurentia, which contains 

 the least amount of chlorophyll, grows near the surface. 

 Lubimenko points out that the mechanism of photosynthesis 

 of the red algae may in some respects be different from that of 

 higher plants, especially in view of the presence of the comple- 

 mentary pigment phycoerythrin. Thus Ulva which contains 

 no complementary pigment has a higher chlorophyll content 

 than Phyllophora. 



It has been suggested by Willstatter and Stoll f that since 

 chlorophyll h (C55H7o06N4Mg) contains more oxygen than 

 chlorophyll a (C55H7205N4Mg), the former compound is pro- 

 duced by the action of chlorophyll a upon carbon dioxide dur- 

 ing assimilation, and that chlorophyll h is then reconverted into 

 chlorophyll a with evolution of oxygen. On the other hand, 

 the molecular formulae of carotin (C40H56) and xanthophyll 

 (C40H56O2) only differ by two atoms of oxygen, and the close 

 association between the carotinoids and chlorophyll may be ex- 

 plained by assuming that the function of carotin is to reduce 

 chlorophyll b to chlorophyll a, being itself oxidized to xantho- 



* Lubimenko : " Compt. rend.," 1924, 179, 1073. See also Wurmser 

 and Duclaux : id., 1920, 171, 1231. 



t Willstatter and Stoll : " Untersuchungen iiber Chlorophyll," p. 237. 



