The underside of the cap bears numerous pure white, plate-like gills that radiate out from the stalk, as shown in the left photo of a portion of a cap. The flat sides of each gill are covered by a layer of spore-producing cells called basidia. Unlike most gilled fungi, the basidia of Amanita bisporiger bear only two spores (basidiospores), instead of the usual four. The basidiospores are borne on the tips of slender, tapered extensions of the basidium called sterigmata. The photo on the right shows a basidium with two sterigmata before spore formation. The shiny, yellowish structures inside the basidium are oil droplets (lipids), which provide energy for the development of the basidiospores.