ABSTRACTThe septal pore apparatus ofTremella globosporawas examined in conventionally fixed and freeze-substituted hyphae. The system of saccules comprising the septal pore cap appears to be derived from several sheets of endoplasmic reticulum. Saccules and endoplasmic reticulum are connected with each other and with the plasma membrane of the septum by a series of electron dense rods. A three-dimensional reconstruction from serial sections of theT. globosporaseptal pore apparatus is presented. Interphase, prophase, and metaphase nuclei fixed with freeze substitution and with chemical fixatives were examined. The spindle pole body inT. globosporais biglobular prior to mitosis. Globular elements expand in volume approximately five fold from prophase to metaphase. The structure of the spindle pole body and of the septal pore apparatus suggest thatTremellaand related taxa may be closely related to those saprobic heterobasidiomycetes with septal swellings and imperforate pore caps.