228 SOME BECENT RESEARCHES IN PLANT PHYSIOLOGY 



action may proceed as before, and that the inhibitor itself 

 may be oxidized instead of the natural or artificial chro- 

 mogen. It was found by the author (1914, 1) that the 

 tissues of the leaf of Iris germanica contain certain areas 

 which fail to give indications of the presence of peroxidases 

 When the whole leaf is pressed, the sap gives no blue 

 colour with guaiacum and peroxide, but sap from the tip 

 of the leaf gives the reaction. Thus the lower portion of 

 the leaf contains an inhibitor, especially in the mesophyll 

 cells, as shown by examination of sections treated with 

 benzidine and a-naphthol. The leaf sap has a powerful 

 reducing action, for potassium permanganate solutions 

 are rapidly decolorized by it even in the cold. This 

 is still effected with cold sap, previously boiled, so is 

 not due to a reducing enzyme. Furthermore, a small 

 quantity of the leaf sap quickly renders the purple sap of 

 the petals colourless, and the addition of hydrogen per- 

 oxide does not restore the colour. This is not remarkable, 

 as the peroxide itself decolorizes the anthocyan of the 

 flower, due, it seems, to the reducing action which it so 

 often exhibits in presence of an easily reducible substance. 

 That this action of Iris leaf sap is a reducing one is 

 made still 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 destroys the blue when the 

 reaction has been brought about before its addition. 

 When, however, Hedera sap is added to Iris sap and 

 guaiacum, it is found that, after a certain quantity has 

 been poured in, the further addition of hydrogen peroxide 

 causes the blue colour to appear. Previous to the 

 addition of Iris sap, the Hedera sap was capable of giving 

 the reaction directly, without the added peroxide. Hence 

 its supply of organic peroxide must have been used up by 

 ; the reducing agent of Iris. 



