628 



Assimilation of Nitrogen hy Bacteria in the Soil. 



different conditions for growth and development in ordinary soil and in a 

 culture solution. 



In order to induce the pure cultures to accommodate themselves to soil 

 conditions, the following method was employed : — Some ordinary garden soil 

 was treated with lime and sterilised in the autoclave. This was then 

 thoroughly wetted with pure cultures of Azotobacter and Psettdomonas, and 

 incuhated at a temperature of 24° C. for 21 days. The organisms multiplied 

 rapidly and spread through the soil, and adapted themselves to the special 

 chemical and biological conditions to which they were subjected. Five 

 grammes of this infected soil were mixed in 100 c.c. of water, to which 

 1 gramme of glucose had been added, and incubated for 24 hours. To test 

 the effect of this culture solution in fixing nitrogen in the soil a series of 

 five earthenware plant dishes were each filled with 5 oz. of rich garden soil 

 which had been air dried and passed through a fine sieve to remove all stones, 

 twigs, etc. Three of the dishes were limed— | oz. of lime to each dish. The 

 dishes were treated as follows : — 



1. Watered with 50 c.c. distilled water. 



2. Watered with 50 c.c. culture solution which had been autoclaved to kill 

 the bacteria. 



3. Watered with 50 c.c. living culture solution. 



4. Watered with 50 c.c. distilled water. 



5. Watered with 50 c.c. living culture solution. 



The dishes were then placed in the incubator and incubated at 24° C. for 

 10 days, the soil being stirred with a sterile glass rod each day for aeration, 

 and each dish receiving 50 c.c. of distilled water on the third, fifth, and 

 eighth days of the experiment, to suj)ply the loss of moisture due to 

 evaporation. 



The nitrogen determinations of tlie contents of the dishes gave the 

 following results : — 



1. 



Limed soil + distilled water 



, , . 324 milligrammes 

 gramme soil. 



N 



per 



2. 



Limed soil + autoclaved culture ... 



330 milligrammes 

 gramme soil. 



N 



per 



3. 



Limed soil + living culture 





per 







gramme soil. 







4. 



Unlinied soil + distilled water 



327 milligrammes 

 gramme soil. 



N 



per 



5. 



Unlimed soil + living culture 



, . . • 352 milligrammes 

 gramme soil. 



N 



per 



