VIEWS OF WILLSTATTER AND STOLL 65 



the absence of the essential enzyme which these authors pos- 

 tulate in the green leaf, and this brings us to the consideration 

 of the mechanism of the action of chlorophyll upon carbon 

 dioxide as visualized by these authors. 



Experiments in vitro have shown that carbon dioxide can 

 form with chlorophyll (I.) in colloidal solution an additive 

 compound of the type of a bicarbonate (II.) as expressed by 

 the equation 



>N f>N 



r\ ;;;iMg*H 2 OC0 2 - R 



>V 

 I 



n 



This compound (II.) cannot be imagined to be capable of 

 parting with two atoms of oxygen with regeneration of chloro- 

 phyll, so that some intramolecular rearrangement must first 

 take place, and this, according to Willstatter and Stoll, in- 

 volves the absorption of energy which is supplied by the sun- 

 light. This change to a formaldehyde peroxide compound 

 (III.) may be illustrated as follows: — 



R 



( 



R 



„/;:-Mg-OCHi 



1>NH 



m 



It is true that experiments in vitro have entirely failed to 

 demonstrate the formation of a peroxide compound by means of 

 horse-radish peroxidase, but this is considered to demonstrate 

 the essential difference between test-tube experiments and 

 the activity of the living cell. Further, there is no doubt that 

 chlorophyll in the chloroplast is protected from photo-oxidation 

 or decomposition by carbon dioxide in a way that chlorophyll 

 in colloidal solution in vitro is not, since the chloroplast will 

 tolerate concentrations of carbon dioxide which decompose 

 chlorophyll in colloidal solution to the magnesium-free com- 

 pound phaeophytin (V.) with precipitation of magnesium 

 carbonate as illustrated by the equation 



C 55 H ?2 5 N 4 Mg + H,0 + C0 2 = C B6 H 7l 5 N 4 + MgCO a 



VOL. II. — 5 



