Enzyme assay showed that the commercial cellulase fromTrichoderma reeseidegraded several polysaccharide substrates; highest activity was on xylan. Transmission electron micrographs showed that theT. reeseicellulase degraded nondecayed wood extensively; the attack always progressed from the point of contact into the cell wall. Cytochemically prepared wood that had been decayed byPoria placentashowed uniform distribution of electron-dense particles throughout the walls; the same results were observed with addedT. reeseicellulase. In wood decayed byGanoderma applanatumwithout or with addedT. reeseicellulase, the progress of degradation was similar to that in nondecayed wood. Negatively stainedT. reeseicellulase had 3–7 nm diameter for the smallest particles; the smallest diamaters of electron-dense particles in wood ranged from 3–7 nm. This suggests that the electron-dense particles probably are cellulase molecu
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