Abstract
Pyrocatechol has been identified as one of two main substances isolated from bark of aspen (Populus tremuloides Michx.) which inhibited Hypoxylon pruinatum (Klot.) Cke. Total inhibition of this fungus was obtained at a dosage of 640 parts per million. Tests with bark extract from two localities showed that inhibition was maximal in samples obtained in the dormant season and from the base of the trees.