H. holstii is the most primitive heterothallic sp. of the genus. Sexually-active mating types are exceedingly scarce among the large numbers of strains isolated from coniferous trees, but rather common among isolates from gums of Prunus. Intensity of the sexual reaction can be greatly strengthened by inbreeding. A diploid culture, designated as NRRL Y-2448, has been produced in the laboratory and used for the production of one of a series of newly discovered phosphomannans produced by primitive species of Hansenula and related sp.