Plant oxydases and the chemical interrelationships of colour-varieties. 469 



True red anthocyanin, on the other hand, is usually without 

 "blueness as measured by alkali, so that an extract gives a reddish- 

 yellow colour with caustic potash or ammonia solution. It is not 

 only with alkalis that the different forms of anthocyanin give different 

 colour reactions but also with other reagents, such as ferric and ferrous 

 salts, ammonium molybdate, sodium phosphate, etc. 



The Interpretation of Mendelian Factors in terms of Oxydases. 



In recapitulation we may now assume that unpigmented parts of 

 plants contain a flavone in solution; from the flavone two classes of 

 oxidised products arise in two stages i. e. the true red and the 

 bluish-red, purple or blue anthocyanins. Such evidence as we possess 

 at present points to the conclusion that this oxidation is the outcome 

 of enzyme activity. The question then arises: How are the Mendelian 

 factors for colour to be interpreted in terms of oxydases? An answer 

 is embodied in the statement that a series of enzymes are concerned 

 in the various stages of colour formation; these enzymes may be 

 expressed as Mendelian factors and their activities are, in many 

 cases, interdependent. 



Thus, for instance, red anthocyanin may be regarded as a more 

 highly oxidised and coloured product of an oxydase (oxygenase-per- 

 oxydase) acting upon a colourless flavone; this oxydase therefore is 

 equivalent to the 'reddening factor' of the Mendelians. Similarly a 

 second oxydase, the Mendelian 'blueing factor', leads to the formation 

 of purple anthocyanin from the product (red anthocyanin) 

 of the action of the reddening oxydase. But the blueing 

 oxydase is unable to oxidise the unaltered chromogen directly. Such 

 an explanation lies within the bounds of our knowledge of oxydases 

 and their functions and certainly affords a working hypothesis for 

 the interpretation of the results of cross-breeding. If the power to 

 form the blueing oxydase is lost from the purple type, a red variety 

 arises, if the reddening oxydase is absent, an albino, which may, 

 however, still retain the ferment capacity of the blueing oxydase. 

 Among the records of cross-breeding there are many instances of 

 reversion to the purple type when a red variety is mated with a 

 white carrying the blue factor. 



One of the most striking phenomena revealed by experiments 

 with Sweet Peas and Stocks is the genesis of coloured offspring from 

 the mating of two albinos. 



