ANTHOCYANINS AND GENETICS 213 



to be one of reduction of a flavone, accompanied by a change of linking 

 of atoms in the molecule, which leads to change of colour. If this 

 should be the case, then the R, factor is a reducing agent. We now 

 await further evidence, and from the preceding paragraphs it should 

 be obvious that the only method of ascertaining the actual relationships 

 between flavones and anthocyanins, and incidentally the nature of the 

 R factor, is to isolate and analyse both these substances from a consider- 

 able number of selected species. 



Let us now turn to the factors controlling the amount of pigment 

 formed. These are the deepening (or full-colour) and diluting factors, 

 and they appear to work for the maintenance of an intermediate type. 

 As a rule, loss of the full-colour factor from the type gives a tinged 

 variety in which little pigment is formed ; loss of a diluting factor from 

 the type gives a deeper variety in which excess of pigment is formed. 

 For the defining of the chemical nature of these factors we have at 

 present no experimental basis. The full-colour factor may control and 

 increase the actual supply of chromogen, and hence niay increase the 

 production of pigment. A second suggestion can be made in connection 

 with the glucoside hypothesis mentioned in the previous chapters. 

 In this hypothesis the idea is that some of the hydroxyl groups of the 

 flavones are combined with sugar, so that the pigment is a glucoside, 

 and it is not until the sugar is split off by a glucoside-splitting enzyme 

 that the reactions which change the chromogen (flavone) to pigment 

 can take place through the vulnerable points of the hydroxyl groups. 

 The control of the amount of free chromogen, and hence pigment, 

 may well be in the power of such enzymes. Or, again, the full-colour 

 factor, in the form of a kind of activator, may increase the oxidation 

 power of the oxidase. 



As regards the diluting factor, it seems not unreasonable to suppose 

 that it is in nature the converse of the full-colour factor; that is, it 

 may limit the hydrolysis of the glucoside, or the oxidising action of 

 the oxidase. But, as we have said, speculation, unless it is in the 

 direction of suggesting lines for research, is not very profitable. An 

 estimation, for instance, of sugar and glucoside content of varieties 

 with different intensities of pigment might lead to some conclusive 

 results. 



Finally, we turn to the factors which modify the colour of the pigment 

 when it is formed. The view is prevalent among botanists in general, 

 as well as among many of those who have worked with anthocyanin, 

 that the variation in colour of anthocyanin, i.e. the shade of red, blue, 



