STUDIES ON SOIL PROTOZOA 



51 



in soil, as determined by the plate culture method, are diminished 

 with an increase in the complexity of the flora. The soils used 

 were all free of protozoa with the exception of those in Group D, 

 yet there is a continual decrease in the number of bacteria found 

 in each group as the number of kinds of bacteria is increased. It 

 will be noted that there was a greater difference obtained in the 

 bacterial counts between Groups B and C, neither of which 

 contained protozoa, than there was between C and D, one of 

 which contained protozoa while the other was free of these organ- 

 It is very probable that this decrease in the number of 



isms. 



TABLE VII 

 Effect of complexity of flora upon the apparent number of bacteria in soil 



Fifteen days 



Average . 



700,000,000 

 580,000,000 

 700,000,000 



660,000,000 



420,000,000 

 420,000,000 

 400,000,000 



413,000,000 



280,000,000 

 250,000,000 

 250,000,000 



260,000,000 



230,000,000 

 200,000,000 

 210,000,000 



231,000,000 



bacteria, due to an increase in the complexity, is only an apparent 

 one and that the actual number of bacteria is just as great as in 

 the soils containing a less complex flora. This view might be 

 explained on the ground that in the more complex flora there 

 was a larger percentage of bacteria which were not able to grow 

 on agar plates. If in two soils each of which actually contained 

 300,000,000 bacteria per gram but in one 90 per cent of the 

 organisms were able to develop colonies on agar plates while in 

 the other only 50 per cent had this property, the counts obtained 

 would be 270,000,000 and 150,000,000 respectively. Since growth 



