258 AGEICULTUKAL AND INDUSTRIAL BACTERIOLOGY 



species of legumes have been suggested. Soil from a field in 

 which a particular legume has been successfully grown is 

 often used for the inoculation of other fields, sometimes 

 being spread at the same time that the seeds of the legume 

 are sown. This method has the obvious disadvantage of 

 great bulk and the chance of introducing undesirable weeds. 

 The second method commonly practiced is that of the use 

 of pure cultures. Some of the agricultural experiment 

 stations in the United States and Canada, as well as certain 

 commercial firms, supply these regularly, usually in the 

 form of a liquid culture. It is customary to supply a cul- 

 ture of the organism isolated from the nodules of the par- 

 ticular legume which it is desired to inoculate. In some 

 cases it is necessary for the organism to be increased. A 

 culture medium containing phosphate, sugar, and water 

 may be inoculated with the culture of the organism it is 

 desired to grow, and within a few hours the numbers of 

 bacteria will greatly increase. Inoculation may be effected 

 by moistening the seeds which are to be sown with such a 

 culture or in some cases by mixing with dry soil and spread- 

 ing this upon the ground to be inoculated. 



Much has been written in bacteriological literature con- 

 cerning the possibility of exalting or increasing the nodule- 

 producing power of particular strains of Rhizobium 

 leguminosarum. This increased power of nodule formation 

 has been termed virulence. It is claimed by certain manu- 

 facturers and by some authors that it is possible by growing 

 in certain kinds of culture media, and by subjecting thq 

 organisms to suitable environment, to increase or decrease 

 this virulence. Adequate scientific demonstrations of such 

 variations in virulence have apparently not been made. It 

 seems that quite as wide variations in inoculating power 

 may be found among various cultures isolated from differ- 

 ent plants of the same legume species. 



Inoculation of soil for growing bacteria has been widely 



