Atkins — Oxydases and their Inhibitors in Plant Tissues. 151 



and excess of lead by sulphuretted hydrogen. The latter was boiled off, and 

 the sugars estimated by Fehling'a solution and the polarimeter as described 

 by Brown and Morris (4). Calculation shows that at the outside no more 

 than half of the osmotic pressure is due to the sugars in Iris leaf sap. From 

 these analyses it will be seen that the sugar concentrations are not such as to 

 interfere with the reaction of the oxydase if present. 



The presence of a strongly reducing substance other than the sugars is 

 shown by the rapid decolourization of potassium permanganate solution by 

 the juice of Iris, even in the cold. This effect is apparently not altered by 

 boiling the juice. A small quantity of the leaf-juice quickly decolourizes the 

 purple sap of the petals, and treatment with hydrogen peroxide does not 

 restore the colour. Hydrogen peroxide alone slowly destroys the purple 

 pigment. That this action of the Iris leaf-sap is a reducing one is made 

 further clear by the fact that not only does it prevent the production of 

 guaiacum blue when added to leaf-sap of Hedera Helix, but it also destroys 

 the blue when it has been already produced by Hedera sap. When, however, 

 Hedera sap is mixed with a little Iris sap and guaiacum, it is found that, 

 after a certain quantity has been added, the further addition of hydrogen 

 peroxide causes the blue colour to appear. Thus the Hedera sap no longer 

 affords the direct reaction, as its supply of orgauie peroxide has been used 

 up by the reducing agent of Iris. The reducing agent is not destroyed by 

 boiling. 



Dialysis of the sap in the presence of toluene was found to remove the 

 reducing agent, for on testing the sap it was found to give the indirect 

 oxydase reaction with guaiacum after dialysis for several days. The next 

 day it was found to give the direct reaction, so apparently some of the 

 organic peroxide remained behind. The sap employed for the dialysis had 

 been filtered tlirough an ordinary filter paper. This dialyzed sap also 

 gave the eatalase reaction. As dialysis proceeded, the effect of the sap 

 upon the purple colouring matter of the petals was tried daily. The leaf-sap 

 which gave the indirect oxydase reaction was found to have altogether 

 lost the power of decolourizing the petal extract. Decolourization was, 

 however, effected by the oxydase of Hedera Helix leaf.' So it appears that 

 either reduction or further oxidation converts the purple pigment into a 

 colourless substance. That the pigment is not merely extracted by alcohol 

 is shown by the alcohol iu contact with a petal becoming first purple 

 and then colourless. Though neutral hydrogen peroxide slowly decolourizes 



' The possibility is not excluded that the oxydase obtains oxygen for oxidation at the expense of 

 the pigment. 



SCIENT. PEOC. R.D.S., VOL. XIV., NO. VII. Y 



