AbstractThalli ofArmillaria melleagrew vigorously and produced abundant rhizomorph after 21 days of incubation on a glucose‐L‐asparagine medium supplemented with auxin, but grew poorly and failed to produce rhizomorphs on a non‐supplemented medium or on one supplemented with either gibberellic acid or kinetin. Replacement of glucose in auxin‐supplemented medium with arabinose, fructose, galactose, maltose, sucrose or starch resulted in poor thallus growth and a lack of rhizomorph development. The superiority of glucose as a carbon source for thallus growth appears to be related to its superiority as a substrate for metabolism byA.