The following precautions are necessary in selecting mushrooms for food: Never eat a “button” mushroom; in this stage wholesome and poisonous mushrooms cannot be properly distinguished from each other. Reject all mushrooms which show signs of a cup or a scaly swelling at the base of the stalk—especially if they have also white spores and a collar. The common meadow mushroom.—The common mushroom (Fig. 157) may easily be found in meadows, especially in autumn and after damp weather in summer. The part which rises above the surface of the ground consists of a stout stalk, about three inches long and perhaps three-quarters of an inch thick. On the upper end of the stalk is a circular horizontal cap, convex and smooth above and concave below; with a diameter about equal to the length of the stalk. The interior of the stalk and cap is composed of a firm white fleshy substance. The underground part of the plant consists of a tangle of [Pg 205] fine white threads, most of which are woven together into strands; and it is easy to see that several of these strands run into the base of the stalk. Each of the fine threads is called a hypha, and the network which they together compose is known as the mycelium. It has indeed been found by microscopic examination that the whole plant is built up of such hyphae—closely packed together in the stem and cap, more loosely aggregated in the underground strands. The stalk of the full-grown mushroom bears, a little above its middle, a ragged ring of tissue—the collar. This ring is the remains of a membrane or veil which in the younger stages reached to the edge of the cap, completely enclosing its lower surface; but which was torn off the cap (Fig. 157) as the stalk of the “button” mushroom elongated. Fig. 157.—Common Meadow Mushroom. To the right, mushroom in “button” stage (× ½). The reproduction of the mushroom.—The lower side of the cap of a mature mushroom bears a very large number of radiating plates called the gills. These are at first pink, but the colour afterwards changes to a dark brown. Each gill produces an immense number of extremely fine spores, too small to be seen individually by the naked eye. When, however, the cap of a mushroom is laid, gills down, on a sheet of paper and protected from draughts, a “spore print” is obtained; the dust of the fallen spores marks the positions of the gills in brown radial lines. Quite recently it has been found possible to raise new mushroom plants by germinating the spores, and there can be no doubt that this is the natural method of reproduction.