The micro-organisms of the soil

by Edward J. Russell; Rothamsted Experimental Station

Y-axis (top right): Bacteria in millions per gramme

Legend: Oicomonas
Species γ
Species α
Bacteria
Temperature
Moisture

It is difficult to resist the conclusion that these annual variations are produced by similar causes, from which it follows that the increase in the numbers of protozoa in the soil is not wholly conditioned by an increased food supply—the bacteria—for the algæ are not dependent on such a form of nourishment. This is substantiated by the fact that the numbers of protozoa, except those of Oicomonas, rose during March, whereas the corresponding increase in the bacteria was delayed till the early part of April.

Fig. 15.—Fortnightly averages of total numbers of Heteromita, Cercomonas, and Dimastigamœba and of bacteria, moisture, and temperature. (From Phil. Trans. Roy. Soc., vol. ccxi.)

X-axis: Fortnight beginning July 1920. Aug. Sep^t. Oct. Nov. Dec. Jan. 1921. Feb. Mar. April May June

Y-axis (bottom left): Percentage of moisture.

Y-axis (top left): Logarithms of numbers of active protozoa per gramme of soil.

Y-axis (bottom right): Temperature F

Y-axis (top right): Bacteria in millions per gramme