Development and Growth

Mushrooms, like other fungi, have no chlorophyll and cannot manufacture their own food. Most mushrooms get their nourishment from decaying organic matter, such as wood, humus, and manure. These mushrooms are saprophytes. A few mushrooms get nourishment, at least in part, from living plants. These mushrooms are parasites.

A typical mushroom has tiny structures called basidia, which produce unicellular reproductive bodies called spores. Under favorable conditions of moisture and temperature, a spore germinates and develops into a mass of white filaments, called a mycelium, which spreads through the organic matter. A mycelium grows for years, lying dormant in winter and dry periods, becoming active when it is moist and warm. Two filaments, or hyphae, of two different mycelia fuse sexually and produce a new mushroomthe fruiting body, or basidiocarp, of the fungus.

Typically, a small, forming mushroom has a rounded shape and is called a button. The button grows rapidly to become the stem and the cap, which together look like a small umbrella. On the underside of the cap are numerous bladelike structures called gills. The gills are initially covered by a membrane, but as the cap grows, the membrane breaks. (The membrane stays attached to the stem below the cap, forming a collar called the annulus.) The gills are lined with basidia, which shoot mature spores into the air to be carried away by the wind. Mushrooms of certain species have pores, or small holes, instead of gills; the basidia are located in the pores.

Gills sometimes change color as the mushroom matures. As the meadow mushroom, a species common throughout North America, matures, its gills change from white to pink to brown. The meadow mushroom is grown commercially and usually harvested before the gills become visible.

Some mushrooms, such as those of the genus Amanita (a group that includes some of the most poisonous species), are completely covered with a membrane when young. As the mushroom grows, the membrane breaks and forms a cuplike structure (the volva) at the bottom of the stem.

Commercially, mushrooms are grown indoors in dark, damp placescellars, caves, abandoned mines, and specially designed buildings. Pieces of specially grown mycelia (called spawn )are placed in beds or trays containing a pasteurized compost of manure or mixture of chopped corncobs, hay, and chemical fertilizers. After five or six weeks the mushrooms appear.