136 On the Formation of Anthocyanin 



pigment. In addition Kati6 has shown experimentally that the pro- 

 duction of pigment, though dependent upon the presence of oxygen, is 

 independent of the presence of carbon dioxide. 



Some important additions to our knowledge concerning the forma- 

 tion of anthocyanin have recently been published by Combes(3). This 

 author has shown that the reddening of leaves is accompanied by an 

 accumulation of oxygen in the tissues and that the disappearance of 

 pigment on the other hand is accompanied by a loss of oxygen. In 

 addition he has shown that red leaves contain proportionally greater 

 amounts of glucosides and sugars than green leaves of the same plant. 

 Combes considers the cause of oxidation to be this accumulation of 

 glucosides and sugars which may arise from various external causes. 

 These substances accelerate the processes of oxidation and hence the 

 gaseous exchange may be fundamentally modified. 



Statement of Hypothesis. 



From evidence which will be given in detail later I have been led 

 to conclude that the formation of anthocyanin from a chromogen 

 depends upon two processes, in which two different enzymes at least 

 are involved. 



The first reaction is reversible and may be expressed as follows : — 

 Glucoside + water ■^*i chromogen + sugar. 



The same enzyme may be supposed to accelerate both the synthetic 

 and hydrolytic reactions. 



The second reaction is one of oxidation and is carried out by an 

 oxidising enzyme or oxidase : — 



Chromogen + oxygen = anthocyanin. 



It must be further assumed that the chromogen can only be 

 oxidised after liberation from the glucoside. 



On the basis of this hypothesis, it follows that the amount of antho- 

 cyanin in any tissue depends upon the amount of free chromogen, and 

 the latter, in accordance with the reveraibility of the first reaction, is 

 directly proportional to the concentration of glucoside and inversely 

 proportional to the concentration of sugar in the tissue. 



The frequent appearance of pigment, under abnormal conditions, in 

 tissues which are normally unpigmented, justifies the supposition that 

 every part of an anthocyanic plant is provided with this mechanism for 

 the formation of pigment. 



