302 Oxydases and Pigments of Plants 



oxydase be destroyed, the only method by which inhibition may be 

 demonstrated must consist in the isolation of the inhibitor, and the 

 addition to it of oxydase. If the latter be destroyed, the evidence for 

 inhibition is forthcoming. If, on the other hand, the inhibitor does 

 not destroy, but only checks the action of oxydase, it should, perhaps, 

 be possible to discover a reagent which, whilst acting destructively on 

 the inhibitor, leaves the oxydase unharmed. Could this be done, the 

 addition of the appropriate reagents should demonstrate the existence 

 of oxydase in the dominant white flower. 



We have pursued our inquiry along the lines suggested by these 

 reflections and have succeeded in demonstrating experimentally the 

 existence of an inhibitor of oxydase in the flowers of Dominant whites. 



As the result of experimenting with various substances, we have 

 found that dominant white flowers, after preliminary treatment with 

 certain reagents, are no longer refractory to benzidine or a-iiaphthol, 

 but give with them well marked reactions for epidermal and bundle 

 oxydases. The reagent which is most efficient in producing this result 

 is hydrogen cyanide. Thus, if a dominant white flower be treated 

 for 24 hours with an aqueous solution of hydrogen cyanide and then 

 washed with water and treated with the oxydase reagent, it gives a uni- 

 form and marked oxydase reaction. A comparative examination of Figs. 

 6 and 8, Plate XIX, shows how striking is the difference in behaviour 

 with respect to oxydase reaction between a dominant white flower placed 

 directly in the oxydase reagent and a similar flower treated previously 

 with hydrogen cyanide. Whereas the former shows scarcely a sign of 

 oxydase, the latter proves itself by the reaction to be rich in that 

 substance. The most satisfactory results are obtained when the following 

 method is practised : 



Immersion of the dominant white flower in a 0'4 per cent, solution 

 of hydrogen cyanide for 24 hours, washing with water, addition of 

 benzidine (alcoholic solution), washing and then adding to the water a 

 drop of hydrogen peroxide. 



Instead of hydrogen cyanide, a saturated solution of carbon dioxide 

 may be employed, but the removal or the destruction of the inhibitor 

 takes place more gradually with this reagent than with hydrogen 

 cyanide (see Fig. 7, Plate XIX). 



Our white-zoned blue flowers provide us with material for verifying 

 the conclusion that hydrogen cyanide brings about the removal or 

 destruction of the inhibitor. If a blue flower with inhibitory patches 

 be treated with hydrogen cyanide in the manner described above. 



