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SUMMARY
A water extract of beechwood (Fagus sylvatica L.) added to a medium containing mineral salts, glucose, “vitamin free” casein hydrolysate, vitamins and purine and pyrimidine bases, stimulates the growth of Polyporus schweinitzii Fr. Three regions of the growth curve are distinguished: Region (A), characterized by a steep slope and induced by smaller amounts of wood extract, a flat portion (B) suggestive of the action of limiting factors, and a region (C) obtained with larger amounts of wood extract and characterized by a steep slope. Evidence is presented that at least two different unidentified growth substances are involved in the growth stimulation in regions (A) and (C).