=424. Beware of the poisonous mushroom.=—The number of species of mushrooms, or toadstools as they are often called, is very great. Besides the common mushroom (Agaricus campestris) there are a large number of other edible species. But one should be very familiar with any species which is gathered for food, unless collected by one who certainly knows what the plant is, since carelessness in this respect sometimes results fatally from eating poisonous ones. [Illustration: Fig. 244. Amanita phalloides; plant turned to one side, after having been placed in a horizontal position, by the directive force of gravity.] =425.= A plant very similar in structure to the Agaricus campestris is the Lepiota naucina, but the spores are white, and thus the gills are white, except that in age they become a dirty pink. This plant occurs in grassy fields and lawns often along with the common mushroom. Great care should be exercised in collecting and noting the characters of these plants, for a very deadly poisonous species, the deadly amanita (Amanita phalloides) is perfectly white, has white spores, a ring, and grows usually in wooded places, but also sometimes occurs in the margins of lawns. In this plant the base of the stem is seated in a cup-shaped structure, the _volva_, shown in fig. 243. One should dig up the stem carefully so as not to tear off this volva if it is present, for with the absence of this structure the plant might easily be mistaken for the lepiota, and serious consequences would result. [Illustration: Fig. 245. Edible Boletus. Boletus edulis. Fruiting surface honey-combed on under side of cap.] =426. Tube-bearing fungi (Polyporaceæ).=—In the tube-bearing fungi, the fruiting surface, instead of lying over the surface of gills, lines the surface of tubes or pores on the under side of the cap. The fruit-bearing portion therefore is “honey-combed.” The sulphur polyporus (Polyporus sulphureus) illustrates one form. The tube-bearing fungi are sometimes called “bracket” fungi, or “shelf” fungi, because the pileus is attached to the tree or stump like a shelf or bracket. One very common form in the woods is the plant so much sought by “artists,” and often called Polyporus applanatus. It is hard and woody, reddish brown, brown or grayish on the upper side, according to age, and is marked by prominent and large concentric ridges. (This form is probably P. leucophæus.) The under side is white and honey-combed by numerous very minute pores. This plant is perennial, that is, it lives from year to year. Each year a new layer is added to the under side, and several new rings usually to the margin. If a plant two or three years old is cut in two, there will be seen several distinct tube layers or strata, each one representing a year’s growth.