Toadstools, or Mushrooms (Agaricacea9 are fungi of the puff-ball kind, consisting of white, branching filaments which creep through the nutriment substance or the host tissues.
Most species are saprophytes, but some are parasites. When the fruits are young they resemble those of puff-balls, but as they grow older a circular layer of spore-bearing tissue develops, and this, by the rapid growth of lower lying tissues, is carried up on a stalk, very much as is done in the stink-horns. (Fig. 27). Here, however, the stalk is formed earlier, and the spores are usually developed after the rupture of the fruit-wall.
A typical toadstool fruit has the following structure: There is first at the bottom the cup shaped remnant of the original fruit-wall (technically, the volva); from this rises the cylindrical stem (stipe), terminating in an ex panded cap (pileus). The stem and cap to gether resemble an expanded umbrella, or a one-legged stool (Figs. 28 and 29), from which latter fact the common name °toadstool° was doubtless suggested. The lower surface of the cap is folded into many vertical radiating plates, called gills (lntold/a), and these are studded with the basidia, bearing the spores. This gill portion corresponds to the circular spore-bearing layer of the stink-horns, and the gills themselves are to be regarded as devices for increasing the number of spores, by an en enlargement of the surface studded with basidia.
While in typical toadstools the cap is rounded and centrally attached to the stem, in see is not the plant itself (that is below the surface) hut it is the fruit of the plant which develops in order that it may produce spores, Pore Fungi (Polyporacecr) are so named because the spore-bearing structure on the under side of the cap of the fruit consists of a mass of small vertical pores, instead of plates, and by this character they may be readily recognized. In typical pore fungi the general structure and development are similar to those of the toadstools, the change from gills to pores being the only important difference. Here, however, many of the species instead of grow ing into regular umbrella-shaped fruits have the stalk more or less laterally placed. In others, again, the lateral stalk is very short, and from this the step is a very short one to its complete suppression, when the cap is sessile marginally, as in the bracket fungi, which are so common on decaying logs and other forms of timber.
Some pore fungi are fleshy, but for the most part they are hard and tough, often resisting decay for many years. Some of the species are perennial, adding successive layers of pore tissue to their fruits for some years.