206 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 6 



concentration of the culture medium and the resistance of 

 organisms to the action of disinfectants afford a definite relation, 

 the greatest resistance being obtained with a culture medium 

 having a hydrogen ion concentration P H 6.0-7.0. 



Fred and Davenport ('18) found that the growth of the 



bacteria 



of different 



reactions was related to the hydrogen ion concentration of the 

 medium. Of the legume bacteria, the organisms of alfalfa were 

 the most sensitive to hydrogen ion concentration, the limit of 

 growth on the acid side being between P H 5.4 and 5.6 ; while, on 

 the contrary, the organisms of lupine were the most resistant, 

 the limit of growth on the acid side being P H 4.6. Sodium 

 hydroxide did not cause any noticeable toxicity towards the 

 legume bacteria until added in greater quantities than N/125 

 and appeared to have only one-tenth the toxic properties of 

 H 2 S0 4 towards these organisms. The authors cite Beijerinck 

 as having secured optimum growth of Rhizobium leguminosarum 

 in N/166.6 acid, but explain the disagreement of results on the 

 ground of employing different culture media. Azotobacter 

 proved to be very sensitive to slight changes of reaction and was 

 able to grow only within the narrow limits, P„ 6.5-8.6. 



Meacham ('18) determined the hydrogen ion concentration 

 of synthetic and malt-extract media necessary to inhibit the 

 growth of Lenzites saepiaria, Fomes rosens, Coniophora cerebella, 

 and Merulius lacrymans. Growth is not inhibited until a very 

 high hydrogen ion concentration is reached, and, while the 

 different fungi show considerable fluctuations, the organisms 

 respond in much the same way. In general, growth proceeds 

 in a straight line until about P H 2.0; decreases almost abruptly at 

 P H 2.6, the range P H 2.6-1.9 being termed the " critical range"; 



om 



H 



decline is more gradual and the limitin 



be about 1.7 



rior to the sudden de 

 maximum of growth 



about 



Kronig and Paul ('97) found a solution of HN0 3 to be dis 

 ictiv more toxic to anthrax snores than the same concentratioi 



of HC1. Their results with acetic acid were 



obtained by Clark ('99) , but the results with 

 consistent with Clark's. 



similar to those 



