Poplar trees with decay typical of that caused by Fomes igniarius, or with extensive stain, were dissected and several hundred platings made from each. Sixty-three different fungi were isolated, as many as 20 from a single tree. Most of the fungi were widely distributed in the tree with no consistent association with any stage of decay. Different zones of decay yielded 19 to 36 fungi each, the zone of early incipient decay giving the largest number. Bacteria were isolated from every zone.Trees with stain but no decay yielded 24 fungi, 15 of which were also found in the decayed trees. Many of these were clearly precursors of F. igniarius. Several pockets of typical decay did not yield F. igniarius, suggesting that it had been killed out by competition.The pH of water extracts of wood from various zones of decay was highly variable, the minimum range for a zone being pH 4.8 to pH 8.8, and the maximum range pH 3.8 to pH 9.4. The implications of these variations are discussed.Effects of various media, and of frozen storage prior to making isolations, were studied.