no BOTANICAL GAZETTE [February 



guaiacol 2 drops (0.025 gm.). Tests for any given set of condi- 

 tions were always run in duplicate, sometimes in triplicate, or even 

 quadruplicate. All experiments were shaken for 3 hours at the 

 rate of 106 complete excursions per minute in a constant tempera- 

 ture chamber provided with a fan driven from the outside, and 

 then allowed to stand for 10-90 hours. Temperature variations 

 were rarely greater than 0.5° during the shaking period, but some- 

 times amounted to as much as 1.0° afterward, owing to less perfect 

 control when the machinery was not in motion. Corrections for 

 temperature variations were made as before by comparison with 

 a blank containing only water. 



Potentiometer measurements were made with a hydrogen 

 electrode like that described by Bo vie (8), streaming hydrogen, 

 3 resistance boxes as described by Michaelis (25, p. 131), a 

 saturated calomel electrode, a normal element checked against 

 another which had been calibrated by the United States Bureau 

 of Standards, and a Leeds and Northrup dead-beat galvanometer. 

 Hydrogen of high purity from a tank of the compressed gas was 

 run through an electrically heated combustion tube containing 

 platinized asbestos and then through the hydrogen electrode tube. 

 The latter, together with the capillary from the calomel electrode, 

 projected through a rubber stopper into the vessel containing the 

 solution to be tested. Escape of hydrogen was provided for by a 

 third opening in the stopper. An error was undoubtedly intro- 

 duced here, due to displacement of CO2 from the solution, in 

 cases where the hydrogen ion concentration was less than io~s 

 (Michaelis, pp. 142-144), but since the only solutions showing 

 this slight degree of acidity were mixtures of bark, water, and pyro- 

 gallol for determination of hydrogen ion concentration before any 

 oxidation had taken place, and since all others were found to be 

 more acid, the error is probably negligible. It could have been 

 avoided entirely by using a Hasselbalch shaking electrode had it 

 and the time for using it been available. 



Among the first experiments run was one designed to test fully 

 the oxidase activity of healthy and diseased bark when pyrogallol 

 was used as the oxidizing substance. The results, given in table II, 

 are the average of 5 closely agreeing determinations. These results 



