ABSTRACTBasidiospore formation inLactarias lignyotellusis a complex phenomenon involving cytoplasmic and wall layer synthesis and interaction. Four stages in early basidiospore development prior to nuclear migration into the spore cytoplasm were delineated, as evidenced by changes in gross morphology, wall tegumentation, and cytoplasmic differentiation. The establishment of early spore asymmetry in heterotropic basidiospores ofL. lignyotelluswas correlated with the presence of a hilar appendix body. The hilar appendix body was poorly differentiated, but appeared to be a demarcated region of cytoplasm that influenced localized spore wall synthesis. The amyloid portion of the spore wall was initiated as an inner, electron-transparent zone. Specialization of the hilar appendix region for forcible discharge was not evident in early spore development inL. lignyotellus.Organelle composition of the cytoplasm throughout early basidiospore development inL. lignyotelluswas comparable to that reported previously for other fungi.