This is a hand-cross-section of a naturally-decaying blade of smooth cordgrass (Spartina alterniflora) containing fungal sexual structures. Phaeosphaeria spartinicola is one of the principal species of ascomycetes that decompose standing-dead blades of smooth cordgrass. This fungus forms its sexual structures (ascomata, the dark brown/black spheroids in this image, about 115 µm diam) just under the abaxial surface (the flat side; the side that usually faces angled-down, and that is the outer side when the blade is furled). The fungus assimilates as much as it can of the leaf mesophyll and fiber tissues, then translocates the assimilate to the sites of ascomatal formation for construction work. A hole is digested out of the leaf-surface material, and the ascoma forms an ostiole (opening) there. When they are mature, ascospores are forcibly expelled from the ostiole out into the air (and/or water?). Some of these will land on and grow hyphae into new blades of smooth cordgrass, completing the cycle. See Newell & Wasowski, 1995, Estuaries 18:241-249; Newell & Porter, 1999, in Weinstein & Kreeger, Concepts and Controversies in Tidal Marsh Ecology, Kluwer.