244 Ingvar Jorgensen and Walter Stiles. 
Chapter II. 
The Pigments of the Leaf. 
A. GENERAL REMARKS. 
It is necessary to review the present knowledge of pigments in 
the 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,C 55 H 72 0 5 N 4 Mg, blue black 
in the solid state, green blue in solution. 
2. Chlorophyll component b, C 56 H 70 O G N 4 Mg, green 
black in the solid state, pure green in solution. 
3. Carotin, forming orange red crystals of the composition 
C 40 H 56- 
4. Xanthophyll, forming yellow crystals of the composition 
^ 40 ^ 50 ^ 2 * 
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 :— 
