F. Keeble and E. F. Armstrong 301 



contain oxydase but lack chromogen. Dominant whites would appear 

 from our biochemical investigation to lack oxydase. Such a conclusion 

 however is not compatible with the known results of crossing Dominant 

 and Recessive whites, and we are driven therefore to seek the interpre- 

 tation of the behaviour of the dominant white races in terms of 

 inhibition of oxydase action. 



It seemed possible that — if inhibition occur — the suppression of 

 oxydase reaction over the white areas might be due to the presence of 

 sugar ; but the application of appropriate tests indicates that reducing 

 sugars are present very generally in the petals of those varieties, coloured 

 and recessive whites, which give good oxydase reactions. We conclude 

 therefore that inhibition is not due to the presence of reducing sugars. 

 Those (heterozygous) plants in which the white areas are ill defined, 

 show the same readiness to give a colour reaction with benzidine or 

 o-naphthol as to develop a blue colouration when in the living state: 

 cf Figs. 13 and 14, Plate XIX, Just as the blue ground colour of 

 the petal may spread into the inhibitory area in the heterozygous 

 plants, so the benzidine reaction may extend over the boundary be- 

 tween the blue, where it is well marked, and the white from which, at 

 first, it is absent. Here again the suggestion of inhibition forces itself 

 on the observer ; for the phenomena are paralleled by those exhibited 

 by heterozygous dominant whites. For whereas pure bred dominant 

 whites have pure white flowers, plants which are heterozygous for the 

 inhibition factor may show a faint tinge or flush of colour over the 

 surface of their petals. 



The results obtained by the investigation of the oxydase contents in 

 dominant white and white-zoned blue flowers, though they suggest the 

 presence of an inhibitor of pigment formation do not, of course, supply 

 actual proof thereof, nor do they indicate the mode of action of the 

 supposititious inhibitor. If the inhibitory substance exist, it should be 

 possible either to remove or destroy it. If we assume the existence of 

 an inhibitor of pigment formation, then we must suppose that it acts in 

 one of two ways. It either inhibits chromogen formation or it checks 

 the action of oxydase. The evidence which we have just produced 

 points to the latter mode of action, for dominant white and the white- 

 zoned blue flowers are unique among varieties of P. sinensis in not 

 giving an oxydase reaction. We will assume therefore that the inhi- 

 bitor exercises its influence on oxydase. That influence may be brought 

 to bear in one of two ways : either the oxydase may be destroyed or it 

 may be prevented from doing the work of pigment formation. If the 



Joarn. of Gen. ii 21 



