THE PLANT OXIDASES 231 



be some ground for the view that inhibitors are very 

 easily oxidizable substances occurring in cells in which 

 there is a physiological lack of oxygen. It must be ad- 

 mitted, however, that it is difficult to reconcile such a 

 theory with their presence in the petals of flowers, such 

 as dominant white varieties of Primula sinensis, where 

 their function has been supposed to be to suppress the 

 formation of anthocyan. In this connection, Molisch 

 (1914) has shown that the heat evolution of the leaves of 

 many species of plants is very considerable, but that of 

 the thallus of Fucus is relatively small. Since, with the 

 exception of traces in the mucilage, oxidases have not been 

 found in this plant, it appears that there may be such a 

 thing as inhibition amounting to the slowing down of 

 oxidation changes to a very marked extent. As the evidence 

 is incomplete and conflicting, it would be unwise to attempt 

 to form any conclusion at the present. 



With regard to the chemical nature of the inhibitors 

 there is no very definite information. Kastle and Loeven- 

 hart (1901) studied the effect of a number of substances 

 in inhibiting or destroying the activity of laccase from 

 the potato. The list includes hydrogen cyanide, phenyl 

 hydrazine, hydroxylamine, sodium thiosulphate, and deci- 

 normal solutions of certain acids. Weak acids, such as 

 carbonic, boric, and phosphoric, have been shown by 

 Bertrand to be inactive at all concentrations. The action 

 of the strong acids and other inhibitors in the same list 

 is probably in a large measure due to their effect upon 

 the oxidases merely on account of the colloidal condition 

 of the latter, for their chemical nature is extremely 

 varied. They give no clue to the possible constitution 

 of the naturally occurring inhibitors. The action of 

 hydrogen cyanide in removing the inhibitor of petals 

 might be considered as pointing to the aldehydic struc- 



