Ultrastructural Morphology of the Hyphal Sheath of Wood Decay Fungi Modified by Preparation for Scanning Electron Microscopy

Our previous attempts to elucidate the structure and extent of the hyphal sheath of wood-decay fungi by scanning electron microscopy (SEM) showed that different preparative methodologies yield differing and frequently conflicting results. Foisner et al. (1985a and b), Highley and Murmanis (1985, 1987), and Green et al. (1989) provided substantial ultrastructural evidence for the presence of extracellular membranous structures that assume a variety of forms, including sheets, tubules, vesicles, and fibers. Evans et al. (1981) reported a fibrillar sheath surrounded by a tripartite pellicle on rapidly growing Bipolaris maydis. Day et al. (1986a and b) also provided evidence for extracellular fungal stuctures, called “fungal fimbriae”, which the authors described as primarily proteinaceous. Foisner et al. (1985a and b) analyzed isolated, extracellular membranous structures, which were reportedly composed of carbohydrate, protein, and lipid. These structures were better visualized by transmission electron microscopy (TEM) after treatment with osmium and/or ruthenium red.