The effect of Bacillus subtilis A13 and Streptomyces griseus 2-A24 on the yield of cereals and carrots was studied. The organisms, both antagonistic to Rhizoctonia solani, were applied individually to barley, oats and wheat for sowing at three sites with a known incidence of R. solani. Root disease was not effectively controlled, yet the seed treatments increased grain yield and dry matter production at one site, advanced time of heading at another site and increased tiller number at two sites. Evidence was obtained that the organisms persisted on pericarps in soil for 5 weeks after sowing. In subsequent trials application of B. subtilis and S. griseus in combination with a pellet treatment increased marketable yields of carrots by 48% and 15% respectively over controls. Addition of the organisms to seed without pelleting increased yields by 17% over controls. These results indicate a non-specific effect of B. subtilis and S. griseus, since they increased growth of plants belonging to two different families, the Gramineae and Umbelliferae, in different soils.

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Summary In assays of acid phosphatase activity with p‐nitrophenyl phosphate as substrate, the low activity found in fluids removed from around roots in liquid medium was not affected by the presence of micro‐organisms. Most phosphatase activity of intact seedling roots was associated with the root surface and was not increased by micro‐organisms in the rhizoplane; in some experiments activity was significantly reduced by soil micro‐organisms. Inoculation of roots with pure cultures of bacteria and a fungus known to have phosphatase activity did not increase this activity of the roots. These results are contrasted with those of other workers. Possible application to the soil situation is discussed.

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