Atkins — Oxydases and their Inhibitors in Plant Tissues. 147 



the petal. The explanation of this behaviour can be given in terms of 

 Keeble and Armstrong's (15) theory, the decolourization being due to the 

 operation of a reducing agent as dehydration proceeds, the oxydase being 

 thrown out of action by the strong alcohol; the restoration of colour on 

 diluting is tlms due to tlie renewal of oxydase activity. The red in the 

 veins is to be accounted for by the diffusion of the natural chromogen into 

 them, thus bringing about contact between the bundle peroxydase and the 

 chromogen. From the fact that the veins are red, not purple, it appears that 

 the natural chromogen is more readily oxidized tlian is a-naphthol, though 

 their intense colour is probably due to a combination of the two colours, 

 for purple becomes visible along the torn edges of the veins. The natural 

 chromogen is apparently oxidized by both the epidermal and the bundle 

 oxydase of Keeble and Armstrong (17). Alcoholic benzidine decolourizes 

 the red petal, and renders it slightly brownish, more markedly so in the 

 veins, and this is brought about without the addition of hydrogen peroxide. 

 P-phenylen diamin in alcoholic solution gives a brown, changing to dark 

 green, the distribution being the same in the red petals as is the colour 

 given by benzidine. With white petals, however, though no colour is given 

 with a-naphthol and hydrogen peroxide, a very faint darkening appears 

 in the veins of petals treated with benzidine and hydrogen peroxide, while 

 ^-phenylen diamin blackens the veins, and causes a slight general discoloura- 

 tion when followed by peroxide. 



Another instance in which the inhibitory action of tannin is clearly 

 brought out is the young and mature leaves of Vitis Veitchii. The sap of 

 the young red leaves shows the direct action with guaiacum, whereas the 

 more mature green leaves, which contain tannin, give no reaction. Young 

 and old, however, both give the epidermal oxydase reaction with alcoholic 

 benzidine, though they give no reaction for the bundle oxydase with 

 a-naphthol. 



With Hedera Helix, however, young and old leaves give the direct action 

 with guaiacum when bruised, the epidermal reaction with alcoholic benzidine, 

 and the indirect bundle oxydase reaction with a-naphthol and hydrogen 

 peroxide. 



The separation of tannin and oxydase had been effected by Aso (2), as 

 the latter is precipitated by strong alcohol. Attempts were made to remove 

 the tannin from the fertile stem of Hqtiiseium Telmateia by means of gelatine, 

 but this was not effective, or at least the enzyme could not be detected in the 

 filtrate. The employment of potassium ferricyanide and ammonia, or of basic 

 lead acetate, is ruled out, for these substances give a blue colour with guaiacum. 



When leaves of Cochkaria armoracia are treated with alcholic a-naphthol 



