Fungi share most fundamental features of cell structure and function with other eukaryotes. Cell biological distinctions include the unique chemical composition of the fungal cell wall and plasma membrane, and the peculiar mechanisms of hyphal growth in filamentous fungi and budding in yeasts. Filamentous fungi generate multicellular colonies, or mycelia, through the extension and repeated branching of cells called hyphae. Mycelia can be restricted to a patch on a decomposing leaf, or span an enormous territory in a forest ecosystem. Fungi also produce multicellular organs that function in the exploration of the environment and survival under conditions of environmental stress. Fruit bodies, including the familiar mushrooms of basidiomycetes, are multicellular reproductive organs. Mushroom formation involves the coordinated growth of millions of hyphae. The molecular control of hyphal growth and fruit body formation are areas of active research, but many questions about the developmental biology of the fungi are unanswered.