What is a special oblong or pyriform cell, with slender branches, which bears the spores in that division of fungi called Basidiomycetes, of which the common mushroom is an example called?

basidium — A special oblong or pyriform cell, with slender branches, which bears the spores in that division of fungi called Basidiomycetes, of which the common mushroom is an example. (Webster's 1913.)