310 IOWA ACADEMY OF SCIENCE 



plant and the sensitive alfalfa plant were chosen for compari- 

 son. The effect of reaction on the reproduction of legume bac- 

 teria was studied in Ashby's mannit solution and in soil. 



In Solution. The plan below was followed : 



1 and 2 — 1.0 per cent of N/1 sulphuric acid. 



3 and 4 — 0.5 per cent of N/1 sulphuric acid. 



5 and 6 — Neutral. 



7 and 8 — 0.5 per cent N/1 sodium hydroxide. 



9 and 10 — 1.0 per cent N/1 sodium hydroxide. 



Ten 500 cc. flasks were innoculated with 1 cc. each of a water 

 suspension of the red clover bacteria. At the end of one and 

 two weeks plate counts were made to show the number of bac- 

 teria in each flask. It was found that a neutral or slightly acid 

 reaction in mannit solution is most favorable for the reproduc- 

 tion of the red clover organism. A slight amount of alkali in- 

 hibited growth. No growth was found in the presence of one 

 per cent normal alkali. The results of repeated counts sup- 

 ported the preceding statement. 



Alfalfa bacteria were studied in the same manner. It was 

 found that Bacillus radicicola from alfalfa grew best in a slight- 

 ly alkaline or neutral solution. The optimum reaction for the 

 growth of the alfalfa organism in mannit solution is some- 

 where between neutral and 0.5 per cent alkali. Unlike the or- 

 ganism from red clover this strain of legume bacteria was found 

 to be very sensitive to acidity. An acid reaction of 0.5 per cent 

 greatly retards growth. After three weeks no living cells could 

 be found. A repetition of this experiment gave similar results. 



In Soil. Twenty-five samples of sterilized Miami silt loam 

 soil were placed in large test tubes and arranged as follows : 



1 and 2 — 1.0 gram of CaC0 3 or four tons per acre. 



3 and 4 — 0.5 gram of CaC0 3 or two tons per acre. 



5 and 6 — Neutral — untreated. 



7 and 8 — 1.0 cc. N/1 sulphuric acid or two tons per acre. 



9 and 10 — 2.0 cc. N/1 sulphuric acid or four tons per acre. 



After treatment the soil cultures were re-sterilized and when 

 cool, were innoculated with a pure culture of legume bacteria. 

 Plate counts were made after one week. The figures of the 



