1. In glass-house trials the influence of residues of clover, grass, and mixtures (1:1) of them added to natural and partially sterilized loam soil upon the parasitic activity of Rhizoctonia solani and the soil micro-organisms and their activity was analyzed. 2. Burying of plant residues (1%) increased the content of organic substance in soil for 8 weeks and longer. 3. The soil reaction (pH) was not noteworthy affected by application of clover or grass residues. 4. However, the populations of bacteria and actinomycetes were increased, especially by adding clover dried. In natural soil, the maximum of stimulation was reached later than in soil sterilized. Adding of grass and roots of grass enlarged the spectrum of fungi observed in the soil amended. Roots of grass stimulated the cellulose-decomposing organisms remarkably. 5. The activity of dehydrogenase (AD) was influenced in different manner: in natural soil fresh clover, grass, mixtures of them, and clover dried increased, and fresh roots of clover, grass, and mixtures of them diminished AD; in soil sterilized the most variants stimulated this activity. 6. All plants residues increased the cellulolytic activity of soil for a long time, but in sterilized soil this effect reached its maximum earlier than in natural soil amended and did not last so long, too. 7. The possible explanations for the inhibition of parasitic activity of Rhizoctonia solani caused by burying plant residues are discussed.