28 



In this table a single plus sign ( + ) indicates feeble or slow ac- 

 tivity, a double plus ( + + ) indicates a strong activity of the kind 

 indicated at the head of the column, and a minus sign (-) indi- 

 cates no activity of the kind. The figures in column II indicate 

 the relative ammonifying activity, and those in column IV the 

 acidifying activity. One important deduction from this table is that 

 the different species vary widely in their ability to accomplish 

 certain work and that cultures of the same species vary greatly. 

 There is therefore opportunity to increase bacterial efficiency in 

 a good soil by selection and introduction of the most effective 

 species and the most effective strains of these species, and to re- 

 duce in number the inefficient and injurious species. The mere 

 making of conditions favourable to a beneficial or desired species 



