This is mycelium of Phaeosphaeria spartinicola, one of the principal species of ascomycetes that carry out the decay of standing-dead parts of smooth cordgrass (Spartina alterniflora). This mycelium was grown in liquid extract of senescent leaves of smooth cordgrass. The hyphae of the fungus forms the core of the filaments seen here (the brighter-edged orange tubes within the more diffuse orange material). The surrounding orange material is the hyphal sheathing. Hyphal sheaths such as this are invisible at the light microscope, even with phase-contrast or interference-contrast optics. The sheaths were made visible here by attaching an immuno-fluorochrome (tRITC), and viewing the mycelium under an epifluorescence microscope. Hyphal sheaths such as these are very important to the functioning of the ascomycete; they serve to retain lignocellulolytic enzymes adjacent to the hyphae, so that the enzymes can dissolve lignocellulose (LC) to the maximum benefit of the LC-digesting fungus. Hyphal sheaths are also believed to serve as one form of protection from desiccation, and they are largely responsible for the high dry-mass densities (e.g., 316 fgC per cubic micron) that have been found for fungal hyphae (i.e., some of the hyphal mass is outside of the hypha itself). The ascospore also has a thin, transparent sheath, the function of which is likely to allow it to adhere at least semi-selectively to blades of smooth cordgrass. See Newell SY, 1992, Estimating fungal biomass and productivity in decomposing litter, pp. 521-561 in Carroll & Wicklow (eds), The Fungal Community. Second Edition. Marcel-Dekker, NY; Newell SY et al., 1996, Lignocellulolysis by ascomycetes (Fungi) of a saltmarsh grass (smooth cordgrass). Microsc. Res & Techn 33:32-46.