2l8 



Journal of Agricultural Research 



Vol. XII, No. 4 



of B. radicicola in sterile distilled water. The cultures were then 

 incubated at room temperature (approximately 25° C.) for eight weeks.^ 



At the expiration of the incubation period the contents of the flasks 

 were poured into hydrometer cylinders of equal depth and diameter. 

 One hundred and fifty c. c. of acetone were added to precipitate the gum. 

 After careful shaking, the cylinders were covered with inverted petri 

 dishes to prevent evaporation. At the end of 24 hours the amount ol 

 gum precipitated was observed. The relative amounts are recorded in 

 Table XXVIII. 



Table XXVIII. — Influence of nitrates on the production of gum by Bacillus radicicola 



From the results it is certain that the nitrates, especially in the smaller 

 of the two concentrates, caused a very considerable increase in the amount 

 of gum produced by B. radicicola. The nitrates of potassium and sodium 

 caused a production of more gum than did the calcium salt. It will be 

 remembered that in the experiments v^rhere the influence of nitrates on 

 the fixation of atmospheric nitrogen by B. radicicola was studied, less 

 nitrogen was fixed in the presence of calcium nitrate than in the pres- 

 ence of the other two salts. Here again the greater stimulative action 

 of potassium and sodium nitrates is emphasized. 



Buchanan in his investigations on the formation of gum by B. radici- 

 cola has found that varying amounts of potassium nitrate in a 2 per 

 cent saccharose solution or in a 2 per cent saccharose-clover-extract 

 solution caused a slight increase in growth and in gum production. 



It seems probable that the increased gum production in the nitrate 

 cultures is caused not only by an increase in bacterial cells but also 

 perhaps by an increased stimulation in the formation of gum by the cells 

 themselves. The relative increase in the amount of gum produced in 

 the presence of nitrates seems to be greater than the actual increase in 

 number of organisms brought about by the stimulating effect of the 

 nitrate. In the latter instance this stimulating effect has been deter- 

 mined in soil cultures only and so a fair basis of comparison can not be 



