[Vol. 6 



204 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



substance (glucose, lactose, etc.), and distilled water, obtained 

 data indicating that streptococci reach more or less definite hy- 

 drogen ion concentration and that there are two limiting zones, 

 P„ 4.6-4.8 and P„ 5.5-6.0. A very large percentage of the 

 streptococci from cases of human infection reached only the 

 lower limit of hydrogen ion concentration, a fact that is very 



striking. 



Morgan and Gruzit ('16) found that soil solutions adjusted 

 to various reactions by N/100 mineral acid and N/100 alkali, 

 when mixed with sterile quartz, showed variations in the type 

 and number of bacteria. A solution with N/1000 alkali gave 

 the best growth while N/1200 acid exerted marked toxicity. In 

 alkaline solutions the number of bacteria increased up to the 

 point of faint alkalinity and then decreased after passing this 

 point; whereas in acid solutions the number of bacteria increased 



with decrease in acidity. 



Zeller ('16) found that the reaction of the medium was a most 

 )ortant factor influencing the growth and metabolism of 



lm 



Lenzites saepiaria. A medium of Thaxter's glucose-potato- 

 hard agar possessing the faintest alkalinity failed to produce the 

 slightest growth, but, on being readjusted to slight acidity, 

 it gave good growth. Spaulding ('11) found that the same or- 

 ganism was unusually sensitive to alkaline media, and obtained 

 luxuriant growth with one-fourth of 1 per cent H 2 S0 4 . Other 

 investigators have published similar results. 



Salter ('16) found that the reproduction of legume bacteria in 

 Ashby's mannite solution and in a soil solution was greatly 



influenced by 



slightly 



acid reaction in mannite solution, the means of determination of 

 which are not stated, proved to be the most favorable for the 

 production of the red clover organism. Inhibition of growth was 

 evident in slightly alkaline solutions, and no growth was found in 

 the presence of 1 per cent nornal alkali. Bacillus radicicola 

 from alfalfa, on the other hand, exhibited great sensitiveness to- 

 wards acidity, retardation of growth being noticed with .5 per 

 cent normal H 2 S0 4 . The organism grew best in faintly alkaline 

 or neutral mannite solution. 



Clark and Lubs ('17) grew Aspergillus niger on a medium con- 





