Carbon Assimilation. 
283 
might combine with another carboxyl group. 1 
From the formulae of chlorophyll given above it will be observed, 
that the phytol component amounts to one-third of the weight of 
the chlorophyll. 
Now analysis of chlorophyll from different plants gave very 
various numbers for the phytol content, and plants yielding 
chlorophyll containing very little phytol were found to be excellent 
material from which to isolate chlorophyll in a crystalline form. 
According to Willstatter and Stoll the chlorophyll in plants is 
accompanied by an enzyme cbloropbyllase, active in alcoholic media, 
which brings about the replacement of the phytol of the chlorophyll 
molecule by alcohol, so that one gets alcoholysis of the chlorophyll. 
The substances so produced were known formerly as crystalline 
chlorophyll. They constitute a group called chlorophyllides. Ethyl 
chlorophyllide (crystalline chlorophyll) is produced according to the 
equation 
(C 32 H 30 ON 4 Mg) (COOCH^) (COOC 20 H 39 ) + C 2 H 6 OH= 
C 20 H 39 OH + (C 32 H 30 ON 4 Mg) (COOCHJ (COOC 2 H 5 ). 
Phytol. Ethyl chlorophyllide. 
Similar chlorophyllides are produced with other alcohols. 
Of much interest is the manner in which the presence of two 
chlorophylls in leaves was discovered. It has been mentioned 
already that the treatment of an alcoholic extract of leaves with 
dilute acid yields a wax-like substance called phaeophytin. It was 
observed by Willstatter that the decomposition of phaeophytin 
results in a considerable number of products, but that these consist 
of two distinct groups, one called the phytochlorins which are olive- 
green in solution, and another group, comprising those which give 
solutions of a beautiful red colour, called phytorhodins. These 
compounds were so numerous that they were simply differentiated 
by letters so that they were designated phytochlorin a, phytochlorin 
b, etc. 
The method by which they were separated by Willstatter and 
Mieg (1906) is based on the different distributions of these substances 
between ether and hydrochloric acid. The concentration of the 
hydrochloric acid determines how much of the substance is extracted 
by it from ether. Thus only traces of phaeophytin a are extracted 
1 In alcoholic solution chlorophyll undergoes a change which Willstatter 
calls allomerisation. He supposes the lactam ring is opened and another 
lactam ring formed. Such allomerised chlorophyll does not give the brown 
phase. This change does not take place in ether or chloroform solutions. 
It is accelerated in alkaline solutions but inhibited by small quantities of acid. 
Therefore, in the separation of the two chlorophylls, a small quantity of 
oxalic acid is added. See section D (6), p. 292. 
