(1) A record of numbers of soil fungi, and bacteria and actinomycetes, in a fallow plot in the Royal Botanic Garden, Edinburgh, was kept over the course of one year, 1937 -1938, together with variations in soil moisture, soil temperature, soil pH, and soil organic matter content.(2) The numbers of soil fungi exhibited a marked seasonal periodicity with a biennial maximum in April and October.(3) The numbers of soil bacteria and actinomycetes exhibited similar fluctuations, but with maximums in May and September.(4) Records of numbers of certain individual species were also taken. Fluctuations in numbers of one or two of the species departed considerably from the mean as indicated by the fluctuations in total numbers of soil fungi.(5) Numbers of fungi developing on agar plates exposed to the air over the soil plot were recorded over the year.(6) The effect of four different soil treatments on soil fungi was investigated. Sterilised dung, nutrient solution, and weak growth caused a significant depression in numbers after 3 months. Sterilised filter -paper had no effect.(7) A new method of distinguishing between fungal spores and fungal mycelium is outlined
