THE OXIDASES IN RELATION TO PIGMENTATION 291 



a chromogen or " phytohaematin," to form a peroxide. 

 The latter is then split up by peroxidase, and its oxygen 

 utilized for the oxidation of reducing substance elaborated 

 by the protoplasm. More recently Palladin (1914) has 

 brought forward the view that the respiration of a substance 

 such as glucose is a hydrolytic oxidation, whereby the 

 carbon is oxidized anaerobically to carbon dioxide, and 

 the hydrogen thus set free combines with a respiratory 

 pigment, reducing it to a colourless chromogen. In the 

 following aerobic stage oxygen is absorbed, with the 

 production of water and the pigment. These processes 

 are shown in the following equations : 



1 . Anaerobic stage : 



Ce H i2O 6 + 6H 2 O+ 12R =6C0 2 + 12RH 2 . 



Glucose. Respiratory pigment. Chromogen. 



2. Aerobic stage: 



12RH 2 + 6O 2 =12H 2 0+ 12R. 



According to this scheme, alcohol, if formed by a zymase, 

 is oxidized further. As shown by Weevers (1911), the 

 action of respiratory enzymes need not involve the pro- 

 duction of alcohol, for in the spadix of an Aroid he found 

 that, even in an atmosphere of hydrogen, respiration of 

 glucose gave rise to carbonic and citric acids. 



Now, if for respiratory pigment in the above equation 

 a flavone, quercetin for example, be substituted, the follow- 

 ing is obtained: 



(a) C 6 H 12 6 + 6H 2 0-r-6C 15 H 10 7 =6C0 2 +6C 15 H 14 7 . 



Quercetin. 



(6) C 15 H 14 7 -H 2 0=C 15 H 10 6 . 



Cyanidin. 



When the change shown in (a) takes place in presence of 

 glucose, the aerobic oxidation may be forestalled by the 

 union of the reduced flavone with the sugar to afford 

 cyanin, the production of cyanidin by elimination of water 



