132 BOTANICAL GAZETTE [February 



Oxidase activity of the fungus in pure culture.— A fungus 

 powder was prepared according to the method employed by 

 Reed (29) from mats of Nummularia mycelium grown in the 

 potato extract medium described by Duggar (19). A test with 

 3 Bunzell tubes using o . i gm. of fungus powder, 4 cc. of i per cent 

 pyrogallol, and i cc. of water gave after 4 days an average mercury 

 rise of 2.35 cm. Quantitative tests on the medium in which the 

 fungus had grown showed ''oxidase" present there also. From 

 these results it appears probable that the greater oxidase activity 

 of diseased bark is due to a summation of the oxidase activity of 

 normal bark and of the canker fungus itself. This may also account 

 for the difference in behavior of the oxidases of the two. 



The general conclusion to be drawn from the preceding data is 

 that diseased bark has greater oxidase activity than healthy bark, 

 probably because of lower acidity and greater degree of dispersion 

 of the oxidizing agent, and because of an actually greater oxidase 

 content. The lower tannin content of diseased bark (see macro- 

 chemical work) may also be a contributing factor, since tannins 

 are known to cause inhibition of oxidase action. This factor is 

 probably eliminated when precipitated oxidases are used. 



In reference to the Bunzell apparatus it may be said that while 

 it gives valuable comparative measurements of oxidase activity, 

 those using it must realize its limitations. Conditions within it 

 are artificial; with reference to hydrogen ion concentration, and 

 probably other inhibiting factors, they are unstable and continually 

 moving toward an equihbrium which, so far as we know, does not 

 coincide with the equilibrium obtaining in the plant. 



Catalase 



Determinations of catalase activity (table XX) were made on 

 12 samples of bark, of which nos. 9 and 10 form a set from one 

 tree and nos. 13 to 20 a set from another tree. Nos. 3 and 4 each 

 came from different trees and are the ones used for most of the 

 oxidase work reported in this paper. They were about i year old 

 when tested for catalase. The other samples were freshly prepared 

 for this work in December 19 17 and January 19 18. The hmbs 

 from which they came were carefully cleaned to remove lichens. 



