If a mushroom is pulled up from the ground a few white strands will be seen clinging to the base of the fungus. These strands form part of the underground tangle of hypha; which represents the mycelium of the mushroom. The hyphas are long and thread-like, and are divided by transverse walls into binucleate cells. The mushroom commences as a small white swelling on the mycelium, which usually grows rapidly and reaches maturity in a few hours.
The fully grown mushroom is an umbrella-shaped structure con sisting of a stalk, or stipe, at the end of which is an expanded head or pileus. A section cut through the stipe and pileus shows that they are made up of closely interwoven hyphae. Radiating out from the stipe on the underside of the pileus are a number of delicate plates called gills. The pileus of the mushroom is the reproductive part, and corresponds in function to the sporangium of Mucor. The surface of the gills is pink at first, but gradually becomes dark purple and covered with small black spores. The interwoven hyphse forming the gills bend outwards towards the surface, and the end cells of the hypha;, termed basidia, bear the spores. A basidium develops two small projections, at the end of which a small rounded spore is formed. When the spores have been set free the basidia wither and their place is taken by others. The spores readily germinate on damp manure or other organic matter in the soil, and give rise to mycelia.
The fungus is a saprophyte living on decaying matter in the soil. The hyphas secrete enzymes which pass through the cell walls, and dissolve part of the organic matter which is absorbed by the hyphae. Mushrooms can be grown from the preparation sold by seedsmen as mushroom spawn. The spawn consists of dried blocks of mixed soil, gelatine and manure in which the mycelium is growing.