Haploid mycelia derived from single-spore cultures may be divided into 2 groups, any member of one being capable of forming a diploid mycelium when crossed with any member of the other. Certain of the crosses produced basidiocarps in culture, some of them abnormal. Evidence presented indicates that some crosses tend to produce abnormal fruiting bodies more than others. Oidia are produced abundantly on both primary and secondary mycelia. Those from primary always germinate to produce another primary mycelium exactly like that upon which they are borne. Of 17 single oidial cultures secured from known crosses, 16 were haploid and 1 was diploid. Of 17 single oidial cultures secured from cultures of polysporous origin, 4 were haploid, 13 diploid.