Plant oxydases aud the chemical interrelationships of colour-varieties. 47 1 



The Inhibitors of Anthocyanin. 



We must fiually turn to the consideration of the causes which 

 prevent the development of pigment and restrict its appearance to 

 h)cal areas only. The inhibition of anthocyanin is, in all probability, 

 brought about by deoxidising- substances in the tissues. Except in 

 the case of certain partially inhibiting- factors, which will be dealt 

 with later, there is no evidence in favour of the existence of special 

 reducing ferments or reductases, of which the sole function is to deprive 

 anthocyanin of its oxygen. Suppression of pigment formation in green 

 leaves, stems and white flowers of anthocyanic species is more likely 

 due to the products of activity of enzymes involved in other metabolic 

 processes connected with respiration and assimilation. Provided the 

 lack of pigment is in some way related to ferment action, we have 

 no difficulty in reconciling this point of view with the Mendelian con- 

 ception of inhibition. The appearance of redleaved varieties of Hazel, 

 Beech, and Primus certainly suggests the loss of a definite factor; the 

 same may be said for the origin under cultivation of fully coloured 

 varieties of Cyclamen persicum, PiHmula acaulis, P. elatior, Bellis 

 perennis, Anemone japonica, Coreopsis and other species in which the 

 flowers of the anthocyanic type are either unpigmented or merely 

 tinged with anthocyanin. In such instances, it might be supposed 

 that the loss of some ferment and the consequent removal of the 

 deoxidising products of its activity would enable pigment to accumu- 

 late in the tissues. The Cocoa-nut and Kaki fruit atford a concrete 

 example of this kind of interaction; for, as previously stated, extracts 

 from these fruits only oxidise guaiacum after the artificial removal 

 of the sugar or tannin as the case may be. 



Inhibition in the above sense has been used in reference to the 

 complete suppression of pigment. There is, however, another series 

 of phenomena illustrating reduction in the amount of pigment which 

 call for a somewhat different explanation. Among several genera, 

 for instance Matthiola, Lathyrus, Primula, and Antirrhinum, it is now 

 a well-established fact that pale varieties are dominant to more 

 deeply coloured varieties, that is there are definite factors in the 

 pale forms which dilute the colour. For these partial inhibitors, it 

 is necessary to postulate some kind of limiting factor or 'reductase' 

 more intimately associated with pigment enzjnues than the general 

 inhibitors appear to be. This distinction is well illustrated by the genus 

 Antirrhinum. The true red variety — rose doré — of Antirrhinum is 

 obviously without the blueing factor; the magenta type, on the other 

 hand, contains the blueing factor. Both type and vaiiety have some 

 pigment in stem and leaves, and just as in the floral organs, the kind 



