332 Journal of Agricultural Research voi. xvi, no. 12 



requirement, however, can ordinarily be carried out only by inoculating sterilized 

 soil, a procedure which does not give rigid proof, but which is fairly conclusive if 

 carried out in connection with the other three requirements. 



The data presented above offer fairly conclusive proof that these con- 

 ditions have all been fulfilled by the organisms in question. The first 

 step in the proof may be found in Tables IX, X, and XI, where it is shown 

 that one or both of the non-spore-forming organisms are always present 

 in active form in manured soil in which ammonification is occurring. That 

 the second requirement is fulfilled is shown by Tables VIII, IX, X, and 

 XI, in which it may be seen that the non-spore formers Ps. fluorescens 

 and Ps. catidatus occur in much greater numbers in decomposing manured 

 soil than in the same soil before the manure has been added, and that the 

 spore former B. cereus occurs in great abundance in the soil before adding 

 manure, but disappears almost entirely after manuring. The isolation of 

 pure cultures, the third step in the proof, needs no comment, while the 

 fourth is fulfilled, as seen by reference to Table XII, where it is shown 

 that pure cultures of the organisms have the power of ammonifying 

 manure in soil.' 



On the basis of the data obtained there are therefore no good reasons 

 for believing that the spore-forming organisms play an important role in 

 ammonifying manure in soil, and there is very good evidence that the 

 non-spore formers _Ps. fluorescens and Ps. caudatus are of primary im- 

 portance in ammonification in manured soils. 



