Corticium effuscatum Cooke & Ellis is heterothallic and tetrapolar. Oedocephaloid conidiophores bearing uninucleate conidia are developed on both haploid and diploid mycelia. Conidia produced on a haploid mycelium germinate only rarely to give new mycelia, but they are able to diploidise a suitable haploid mycelium when in association with it. A small percentage of the conidia produced on a diploid mycelium germinate to give haploid mycelia, part of which are identical in pairing reactions with one parent, the remainder with the other parent. Chlamydospores are produced on haploid and diploid mycelia and reproduce the generation on which they are borne.