The fine structure of the basidiospores of Pluteus cervinus and Agrocybe acericola is described using TEM, SEM, and light microscopy.The basidiospore wall of Pluteus cervinus is bipartite. No surface ornamentation or germ pore is present. The protoplasm is surrounded by a typical membrane which lacks distinct invaginations. Spores contain much stored lipid, which is centrally located. Spores are uninucleated with the nucleus closely appressed to the cell membrane, located at the base of the spore near the hilar appendage. Mitochondria with few, well-delineated plate-like cristae are present. Endoplasmic reticulum (ER) is scant. Ribosomes occur regularly attached to the ER and outer mitochondrial membrane, as well as being densely packed throughout the cytoplasm. Various sized vacuoles containing an electron dense material are present. Microbody-like organelles are observed, which are probably glyoxysomes, since assays of malate synthase, a maker enzyme of the glyoxylate cycle, are positive.The basidiospore wall of Agrocybe acericola is composed of two distinct layers, both layers are continuous around the spores, at the germ pore the outer wall is very thin and the inner wall becomes thicker. The plasma membrane is appressed to inner wall and lacks invaginations. The protoplasm is densely packed with small granules, probably ribosomes and/or glycogen. Spores contain very little lipid with bipolar distribution. Mitochondria are well-defined and distributed in cytoplasm. Spores are binucleate with the two nuclei lying on a line nearly perpendicular to the long axis of the cell. Various size single membrane-bound vacuoles are widely distributed in the cytoplasm. These vacuoles were shown to contain acid phosphatase indicating lysosomal activity. Microbodies, probably glyoxysomes, are observed. Malate synthase assays are positive indicating the occurrence of the glyoxylate cycle. / Department of Biology

Morphologically and anatomically the Russulales (Basidiomycetes) are a homogeneous group of higher fungi, which contains both ballistosporic and statismosporic, agaricoid and gasteroid taxa. Spore symmetry and ability to forcibly discharge spores are therefore fundamental systematic characteristics in the Russulales. Ballistosporic and statismosporic basidiosporogenesis however, has not been critically compared. Early and late basidiosporogenesis, spore-wall tegumentation, and differentiation of the hilar appendix were ultrastructurally characterized in species selected from eight genera of agaricoid and gasteroid Russulales including: Russula, Lactarius, Macowanites, Arcangeliella, Elasmomyces, Gymnomyces, Martellia, and Zelleromyces. Six spore-wall layers are present in developing spores in all genera. Two wall layers are associated with an evanescent pellicle and four wall layers are derived from the sterigma and young spore. The amyloid portion of the spore wall in the Russulales is an electron-translucent wall layer covered by an electron-dense surface layer. Ontogeny of spore-wall ornamentation is similar in all genera, however diversity in the degree of ornamentation and amyloidity results from differentiation and intermixing of the two outermost enduring wall layers. Establishment of early spore asymmetry in both ballistosporic- and statismosporic-heterotropic basidiospores is highly correlated with the presence of a hilar appendix body. Observation of a demarcated cytoplasmic region, reminiscent of the hilar appendix body, in asymmetric sterigmata of orthotropic Russulales suggests that basidiospore morphology and symmetry are variable features in the Russulales. Late spore development subsequent to nuclear migration is similar in orthotropic and heterotropic Russulales. Orthotropic basidiospores appear to be released from sterigmata upon breakdown of the sterigmata. Heterotropic basidiospores are released while sterigmata are intact. Plugging layers develop in both the sterigma and in the hilar appendix. The hilar appendix plugging material appears to be produced by a plug-forming body which originates in the spore, and possibly controls liquid droplet formation during ballistosporic discharge. Ballistosporic discharge appears to be a conservative phenomenon in most Basidiomycetes resulting from a prescribed sequence of biochemical and developmental processes. The use of ballistospory and statismospory in distinguishing families and genera must be re-evaluated in the Russulales. Recognition of the Lactariaceae and Russulaceae is discussed. / Ph. D.