THE PIGMENTS OF LEAVES. f 

 THE CHLOROPHYLLS AND CAROTINOIDS. 



The work of Willstatter and his pupils dating from 1906 upon the com- 

 position and constitution of the pigments in plant leaves has greatly in- 

 creased our knowledge of this most complex and difficult subject. Willstatter, in 

 conjunction with Stoll, has summarised his results in book form l and presented 

 us with his conception of the chemistry of these pigments. The close 

 analogy which was believed to exist between chlorophyll and haemoglobin, 

 though it differs in detail, is confirmed. Chlorophyll, like haemoglobin, 

 consists of substituted pyrrole nuclei. 



Four pigments are contained in the chloroplasts of the leaf : 



Chlorophyll a C B5 H 72 O 6 N 4 Mg 

 Chlorophyll b C 65 H 70 O 6 N 4 Mg 

 Carotin C^H,^ 



Xanthophyll C^H^O-j 



Chlorophyll and fucoxanthin, C^H^Og, are the pigments of the brown 

 algae. 



Fresh leaves contain about -2 per cent, of chlorophyll a, 75 per cent, of 

 chlorophyll <, "33 per cent, of xanthophyll and '155 per cent, of carotin. 



Chlorophyll a and 6. 



The two chlorophylls have a very similar composition and differ only by 

 the replacement of two hydrogen atoms in a by an oxygen atom in b. Both 

 contain magnesium in organic combination and both are acid esters of a tri- 

 basic acid, termed chlorophyllin, with (i) phytol, C 2 oH 39 OH, an unsaturated 

 primary alcohol with a branched chain of carbon atoms, whose constitution is 

 unknown but is represented by 



CH 3 . CH . CH . CH . CH . CH . CH . CH . C =C . CH 2 OH 



CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 . 



(2) methyl alcohol. 



They are esters of chlorophyllin, i.e. methyl phytyl chlorophyllides. 



1 " Untersuchungen iiber Chlorophyll," Berlin, 1913. 

 519 



