THE COMPOSITION OF CHLOROPHYLL 235 



four distinct components, viz. a-chlorophyll, b-chlorophyll, 

 carotin, and xanthophyll. The chemical formulae for 

 these pigments, as given by Willstatter, are : a-chloro- 

 phyll, C 55 H 72 O 5 N 4 Mg, blue green in tint ; b-chlorophyll, 

 C^H^Oe^Mg, pure green or yellow green ; carotin, 

 C 40 H 56 , orange red ; xanthophyll, C 40 H 56 O 2 , yellow. This 

 was the composition of leaf green found in every case 

 submitted to analysis. The only metal present was 

 magnesium, and neither iron nor phosphorus could ever 

 be detected, thus ending the long-drawn-out controversy 

 as to the presence or absence of these elements that 

 had taken place during the latter half of the nineteenth 

 century. Willstatter also found that in 100 parts of 

 dry leaf substance about 0-6 was composed of a-chlorophyll, 

 about 0-2 of b-chlorophyll, about 0-07 to 0-12 of xantho- 

 phyll, and about 0-03 to 0-08 of carotin, and that they 

 were invariably accompanied by sundry fatty or waxy 

 impurities which had to be separated off before research 

 could be carried out on the pigments themselves. Will- 

 statter came to the conclusion also that chlorophyll 

 occurs in the leaf in the colloidal condition, for the position 

 of the bands in the absorption spectrum of fresh leaf green 

 coincided exactly with the position of those of a colloidal 

 solution of the pure a-chlorophyll. 



Willstatter also examined the pigments of Algae and 

 compared them with those extracted from Phanerogams. 

 He found the same four pigments in Chlorophyceae, 

 although the proportional amounts differed, while in 

 Phaeophyceae he demonstrated the presence of a-chloro- 

 phyll, traces of b-chlorophyll, and also of carotin and 

 xanthophyll, but established the existence of a third 

 yellow pigment, fucoxanthin, which had a formula, 

 C 40 H 56 O 6 , while all the yellow pigments were relatively 

 much more abundant than in Phanerogams. 



The influence of acids and alkalies on the green pigment 

 had occupied the attention of many workers during the 

 preceding years, and the decomposition products had been 



