Morphology

A mushroom develops from a nodule, or pinhead, less than two millimeters in diameter, called aprimordium, which is typically found on or near the surface of thesubstrate. It is formed within themycelium, the mass of threadlikehyphaethat make up the fungus. The primordium enlarges into a roundish structure of interwoven hyphae roughly resembling an egg, called a button. The button has a cottony roll of mycelium, theuniversal veil, that surrounds the developing fruit body. As the egg expands, the universal veil ruptures and may remain as a cup, orvolva, at the base of thestalk, or as warts or volval patches on the cap. Many mushrooms lack a universal veil, therefore they do not have either a volva or volval patches. Often, a second layer of tissue, thepartial veil, covers the bladelikegillsthat bearspores.