vn] THE FORMATION OF ANTHOCYANINS 117 



which the products of synthesis pass from the leaves, may cause red- 

 dening in the portion distal to the point of injury. Analyses, made 

 by Combes (207) of leaves of Spiraea which had turned red owing to 

 decortication, show that red leaves contain greater amounts of both 

 glucosides and sugars to the following extent: 



Glucosides Sugars 



Green leaves ... ... 1-64 2-21 



Red leaves 6-15 4-26 



and that the increase of glucoside in red leaves is proportionally greater 

 than the increase of sugar. When we assume also that the chromogen 

 (flavone) is being continually synthesised in the leaves from sugar (see 

 p. Ill), then it follows that in red leaves the hydrolysis reaction, owing 

 to the increased concentration of the glucosides, may take place in 

 the reverse direction : 



glucoside + water -*- chromogen + sugar 



Hence more free chromogen and consequently more pigment will be 

 formed. 



5. Evidence from data as to the absorption of oxygen in gaseous exchange 

 in red and green leaves. By making analyses of gaseous exchange in 

 red and green leaves respectively, Combes (379) has shown that the 

 red absorb more oxygen during the reddening process than the normal 

 leaves. Katie (354) also demonstrated that leaves kept in culture 

 (sugar) solutions in the absence of oxygen, failed, although they remained 

 alive, to form any anthocyanin in contrast to similar leaves when the 

 experiments were conducted in air. Molliard (376) also showed that 

 oxygen is necessary for the formation of anthocyanin in radishes by 

 totally submerging the roots in sugar solution, under which conditions 

 the pigment failed to appear. 



That anthocyanin is produced by the action of an oxidase on a 

 chromogen forms the basis of the hypothesis of Keeble, Armstrong 

 & Jones (230, 231). It would appear to be evident from the results 

 obtained by these authors that there is an intimate relationship between 

 the distribution of oxidase and the development of anthocyanin. 

 There is every reason to believe, on their evidence, that oxidation 

 processes would readily take place in those tissues in which anthocyanin 

 is found. These authors consider that the formation of anthocyanin 

 is represented by the following equation: 



glucoside + enzyme -*- sugar + chromogen 

 chromogen + enzyme -+- peroxide -- pigment 



