36 



Journal oj Agricultural Research voi. xvi, no. 



Table IV. — Effects of variable moisture on bacterial content of five typical acid soils 



o Incubated 10 days in carbon dioxid; then 10 days in air. 

 * Sum of air and hydrogen incubation, 

 c All figures were computed from 5 plates. 



The bacterial content, as well as the proportions of aerobes to anaerobes, 

 was changed by the degree of saturation of the soil, but the nature of 

 the soil had a greater effect than the moisture content on bacterial num- 

 bers. The proportions of anaerobes to the aerobes which survived 

 •carbon-dioxid incubation increased with soil organic matter when the 

 soils were held under optimum moisture conditions. 



Plates 5 to 9 show representative petri plates from the i to 40,000 

 bacterial dilution of these soils. Figures A^, H^, and C^ in each plate 

 show representative petri plates after air (A) , hydrogen (H) , and carbon- 

 dioxid, then air (C) incubations of bacterial dilutions of samples from 

 pots of soils kept one-fourth saturated with water. Figures Aj, H2, and 

 C2 are from samples from pots of soils kept half saturated, while A3, H3, 

 and C3 are from pots of soils kept fully saturated with water. 



Plates 5 to 9 show that the bacterial flora of each soil is different from 

 that of every other soil. The soils kept one-fourth saturated with water 



