SOME RECENT WORK ON PLANT OXIDASES 119 



the young leaves of the Virginian creeper (Vitis Veitchii) are 

 red, and give the oxidase reactions. The mature leaves are 

 green and give no oxidase reactions ; but in them tannin 

 is present, which is known to act as an inhibitor. Finally, 

 in autumn the leaves again become red, yield positive results 

 with oxidase reagents, and contain no tannin. Another instance 

 examined by the author l is the behaviour of the leaves of Iris 

 germanica, which contain reducing substances in quantity, 

 and fail to reveal oxidases in the pressed sap, though micro- 

 scopic examination of sections treated with the usual reagents 

 demonstrates their presence in certain tissues. Moreover, on 

 pouring the sap into alcohol a precipitate is obtained. When 

 this is well washed with spirit and redissolved in water, it 

 is found to give the guaiacum reaction for an oxidase. The 

 inhibitor here cannot be an anti-enzyme of colloidal nature, 

 for after dialysis of the sap in presence of toluene a direct 

 oxidase reaction can be obtained with guaiacum. In Pteris 

 aquilina leaf sap too, removal of an inhibitor by dialysis 

 permitted the detection of an indirect oxidase reaction. 



In the course of their researches on the production of antho- 

 cyan pigments, Keeble and Armstrong 2 showed that certain 

 white flowers owed their colour to the presence of an inhibitor 

 which prevented the action of an oxidase. These authors 

 observed that treatment with dilute hydrocyanic acid and subse- 

 quent thorough washing neutralised the action of the inhibitor, 

 so that the oxidase now afforded the usual reactions. I have 

 also found their method effective with the flowers of a number 

 of varieties of Iris, 3 and with the tissues of certain fruits. Thus 

 it is clear that in numerous instances the occurrence of the 

 oxidase may be demonstrated by a variation of the usual pro- 

 cedure, and so negative results must be accepted with caution. 



With regard to the oxidases of the fresh water and marine 

 algae, however, but little is known. It has recently been shown 

 by the author 4 that oxidases of the phenolase type at least are 

 very infrequently met with in this class of plants. Out of about 

 thirty species of the green, brown and red marine algae only six 

 were found to contain oxidases. Brown algae of the Laminaria 



1 Atkins, W. R. G., loc. cit. 



3 Keeble and Armstrong, Proc. R. Soc. 191 2, 85 B, 214. 



3 Atkins, W. R. G., Set. Proc. R. Dubl. Soc. 1914, 14 (N.S.), No. 8, 157. 



4 Ibid. 1914, 14(N.S.), No. 11, 199. 



