208 



Journal of Agricultural Research 



Vol. XII. No. 4 



nitrate media, while the control culture was still free from them. The 

 third day showed the presence of volutin bodies in all four cultures. 

 Strain B offers the better proof that sodium nitrate tends to hasten the 

 appearance of volutin bodies in the cells of Azotobacter. Further 

 experiments were not made in an endeavor to determine what influence 

 nitrates might have on the cytology of the Azotobacter cell. The brief 

 studies reported here were made in connection with the pigment forma- 

 tion experiments, but do not bear any particular relation to them. The 

 increase in number and size of volutin bodies may bear some relation to 

 the increased amount of nitrogen fixed or assimilated by Azotobacter in 

 the presence of nitrates. 



INIflvUENCE OF NITRATES ON BACILLUS RADICICOLA 



INFLUENCE OP NITRATES ON THE GROWTH AND REPRODUCTION OF BACILLUS RADICICOLA 



IN STERILIZED SOIL 



One hundred and fifty gm. (dry weight) of the soil were weighed 

 into 500-c. c. E^rlenmeyer flasks and the nitrates added as indicated 

 in Tables XX-XXII. Duplicate cultures for each amount of nitrate 

 were prepared. One per cent of mannit (in 5 c. c. of distilled water) 

 was also added. The flasks were kept at room temperature for one 

 day and the contents then thoroughly mixed. The flasks were steri- 

 lized at 15 pounds' pressure for three hours. Upon cooling they were 

 inoculated with 5 c. c. of a suspension of Bacillus radicicola in sterile 

 distilled water. The number of bacteria in the inoculum was deter- 

 mined. The moisture content was then approximately 18 to 20 per 

 cent. The flasks were incubated at 28° to 30° C. and mannit-agar 

 plates poured at the end of one and two weeks. The results of these 

 experiments are given in Tables XX, XXI, and XXII, in which each 

 figure represents an average of duplicate plates. 



Table XX. — Influence of potassium nitrate on Bacillus radicicola in sterilized soil 



a Contamination, 



