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Discoloration tests with wood meal and wood extracts showed that red heart of white birch (Betula papyrifera Marsh.) is the result of a n enzymatic oxidation. Pyrocatechol, coniferyl alcohol, pyrogallol, and catechin, compounds found to be substrates for the staining process, were identified by thin-layer chromatography and ultraviolet spectrophotometry. Evidence was obtained that pyrocatechol, coniferyl alcohol, and pyrogallol are present in the heartwood as glycosides, whereas catechin occurs as a free compound. The reddish-brown stain of the wood is due to the oxidation products of the phenols involved.Fungi associated with red heart are the main producers of phenol oxidases which catalyze the discoloration process. The ability of Trichocladium canadense Hughes (= Torula ligniperda (Willk.) Sacc.) to cause red heart in white birch is questioned.'Present address: c/o CIBA

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