64 BOTANICAL GAZETTE [JULY 
formation of carbon dioxide and acetic acid; salts of mercury, 
silver, and gold oxidize pyrogallol to acetic and oxalic acids. It 
might appear that oxidation in the larger BUNZEL apparatus, when 
the alkali basket is used, is greater because of the removal of carbon 
dioxide, which would tend to increase the acidity if allowed to 
remain. This can hardly be true, however, since carbonic acid 
has a low dissociation constant and at the temperature of these 
experiments would be present in the solutions in comparatively low 
concentration. Its effect on acidity is but slight at best, and the | 
removal of it merely shortens the time required for the reaction 
to come to an end. Acetic and oxalic acids are both more impor- 
tant, for two reasons: all of the acid formed remains in solution, 
and if it is acetic acid, dissociation (and the consequent inhibitory 
_ effect) is about ten times as great as for carbonic acid. 
An H* concentration of 1073 or 107~¢ is just in the midst of H™ 
concentration optima for various enzymes, as given by HOBER (6, 
p. 721), varying from 107? 5 for pepsin to 10~*'5 for esterase of the 
blood. No data are given for oxidase, but the work here reported 
on indicates that the optimum for them is much less than 107°. 
If the pyrogallol as used in the apparatus is just about the H™ 
optimum, it is easily seen how the plant juice could make the H™ 
concentration too high. Then when base is added, the strongest, 
most highly dissociated acids are heutralized first, and the 2 Be 
concentration drops faster than represented by the degree of 
neutralization. : 
It may be possible to get some idea of the H* optimum for 
oxidase activity, and of the H* concentration of various mixtures 
in the apparatus by further work with indicators, but definite 
knowledge on these points must come finally from careful deter- 
minations by the gas-chain method. 
Summary 
1. Extract of apple tree bark affected with Illinois canker 
causes greater and more rapid oxidation of pyrogallol than does the 
extract of healthy bark. 
2. Diseased bark extract is less acid than healthy bark 
extract, according to both indicator and titration figures, hence the 
