Cellulase activity of Polyporus betulinus

Methods are described for isolating and crossing monocaryons of P. betulinus and of determining their cellulase activity by observing changes in viscosity of a carboxy-methyl cellulose preparation. Cellulase activity, so measured, is not correlated with growth rate in the presence or absence of cellulose. Cellulase activity is almost certainly controlled polygenically and is inherited independently of mating type.