134 On the Formation of Anthocyanin 



in any species, the greater the number of derivative varieties we may 

 expect to appear under cultivation. Only an exact knowledge of the 

 chemical reactions involved in the formation of pigment will enable us 

 to explain the mechanism of colour inheritance and the cause of differ- 

 ences between varieties. 



The main conclusions arrived at in the present paper may be 

 summarised as follows : — 



(1) The soluble pigments of flowering plants, collectively termed 

 anthocyanin, are oxidation products of colourless chromogens of an 

 aromatic nature which are present in the living tissues in combination 

 with sugar as glucosides. 



(2) The process of formation of the glucoside from chromogen and 

 sugar is of the nature of a reversible enzyme action : 



Chromogen + sugar '*~~^ glucoside + water. 



(3) The chromogen can only be oxidised to anthocyanin after 

 liberation from the glucoside and the process of oxidation is carried out 

 by one or more oxidising enzymes : 



Chromogen + oxygen = anthocyanin. 



(4) From (2) and (3) we may deduce that the amount of free 

 chromogen, and hence the quantity of pigment formed at any time in 

 a tissue, is inversely proportional to the concentration of sugar and 

 directly proportional to the concentration of glucoside in that tissue. 



(5) The local formation of anthocyanin which is characteristic of 

 the normal plant is due to local variation in concentration of either 

 the free sugars or the glucosides in the tissues in which the pigment 

 appears. The abnormal formation of pigment under altered conditions 

 is due to differences in the concentration of these same substances due 

 to changes in metabolism brought about by these conditions. 



(6) On the above hypothesis the formation of anthocyanin is 

 brought into line with that of other pigments produced after the 

 death of the plant, as, for example, indigo, the respiration pigments of 

 Palladin, etc. 



Results obtained by Previous Investigators. 



Although the soluble pigments of plants have afforded material for 

 a considerable amount of investigation, the sum total of results gives 

 us very little knowledge either of the composition of these substances 

 or of the processes which underlie their formation. 



