Scanning electron micrograph of the undersurface of a cultivated mushroom (a fungus) looking edge- on at the gills of a closed button. The cultivated mushroom is closely related to Agaricus bisporus; so-called because its basidia (the spore bearing structure of some fungi) produce two spores (instead of the usual four), as do those of the edible mushroom. Basidia form a feritle layer called the hymenium, which covers the gills. The furry appearance of the gills here indicates the basidia. Magnification X90 (at 10x8 size).