3. The gills and spores.—Cut the stalk across at the top, and make a drawing of the lower surface of the cap. Notice the radiating vertical plates (the gills), and their flesh-coloured or dark-brown tint. Be careful to show the exact arrangement of the gills in, say, a quarter of the drawing. Cut off the cap of a mushroom which has brown gills and lay it, gills down, on a sheet of paper; cover it with a tumbler to shield it from draughts, and leave it for a day. Then take off the cap (being careful not to smear it along the paper), and observe the radiating brown lines. On touching them, it will be seen that the lines consist of fine brown dust. The particles of dust are spores. They have evidently fallen from the gills.
4. The source of the mushroom’s food.—What is the colour of the mushroom? Cut through the stalk and cap in various directions and notice the pure white “flesh” of the interior. Do you think it likely that the plant can obtain carbonaceous food from the air? Why not? Dry a mushroom and burn it carefully. Does it contain carbon? Where must the carbon have come from, if not from the air. Can you find any decaying vegetable or animal matter in the soil in which mushrooms grow?
5. Toadstools.—Carefully compare the common mushroom with other gilled fungi which look somewhat like it. Notice particularly the following characters: the colour, shape, and texture of the surface of the cap; the colour and arrangement of the gills; the proportions of the length and thickness of the stalk to the diameter of the cap; the presence or absence of a collar on the stalk; the presence or absence of a cup, or scaly swelling, at the base of the stalk.
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 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.
The method of life of the mushroom.—The mushroom, like all the plants we have studied, thus consists of parts which perform one or other of two duties; that of feeding the plant, and that of continuing the race. In this case the food is supplied entirely by the underground mycelium; while the aërial part, consisting of stalk and cap, is concerned only with the work of scattering the spores. There is nothing corresponding to the leaf-green of the higher plants, and the mushroom is therefore unable to make use of the carbon dioxide of the air ([p. 34]) as the source of the carbonaceous food which is necessary for its life. Carbonaceous and mineral food alike are obtained from the soil by the underground mycelium. The plant is, in short, dependent upon carbonaceous food which has been previously built up by some other plant or animal, and can therefore grow only in soil containing decaying animal or vegetable matter. It would be quite unable to subsist upon the nutritive solution of salts which was seen ([p. 29]) to suffice (when supplemented by fresh air) for green plants.