The Pigments of the Leaf. 5 



Chaptek II. 



The Pigments of the Leaf. 



A. General Remarks. 



It is necessary to review the present knowledge of pigments in 

 tlie leaf before discussing the actions taking place there, more 

 particularly as this knowledge has been considerably increased 

 during recent years by the researches of Willstatter and his co- 

 workers, and as the results of these researches do not appear as 

 yet to have penetrated very deeply into the botanical world. 



Willstatter's researches have extended over a period of more 

 than ten years, during which time he has been assisted by many 

 expert chemists, working under conditions which have enabled them 

 to conduct experiments on a properly large scale. The result is 

 that the chemistry of chlorophyll has been made at least as clear 

 as that of any other plant substance, and there is every reason to 

 hope that in applying the experience of Willstatter and his 

 colleagues to experiments in plant physiology, great progress will be 

 made. 



Besides working out the chemistry of the leaf pigments and 

 isolating them, Willstatter has made a large number of analyses of 

 pigments from various species of different families, from plants 

 growing under different ecological conditions, and from plants 

 collected at different seasons and at different times of day. 



The main facts derived from Willstatter's researches are that 

 the chloroplasts contain four pigments, two green and two yellow. 

 These are: — 



1. Chlorophyll component a, CJ5H72O5N4 Mg, blue black 



in the solid state, green blue in solution. 



2. Chlorophyll component b, C05H joOgN^Mg, green 



black in the solid state, pure green in solution. 



3. Carotin, forming orange red crystals of the composition 



4. Xanthophyll, forming yellow crystals of the composition 



It was found that these pigments were identical in all plants exam- 

 ined. The chlorophyll always contained 2-7% of magnesium, which 

 is the only metal present in its ash. Neither iron nor phosphorus 

 is present. 



In fresh leaves these four pigments were found in about the 

 following quantities : — 



