Let us take a specimen of one of the most perfectly formed and highly developed fungi, the common, shaggy mushroom, for instance (Agaricus procerus), which is also the most familiar example, and endeavor to point out the peculiarities of its structure. Like all plants, it consists of two distinct parts, the organs of nutrition or vegetation and the organs of reproduction; the former bearing but a very small proportion in size to the latter. The organs of nutrition or vegetation consist of grayish-white interlacing filaments, forming a flocculent net-like tissue, and penetrating and ramifying through the decaying substances on which the mushroom grows. These filaments are formed of elongated colorless cells. They are developed under ground, and in other plants would be called roots. This part of the fungus is called by botanists mycelium, and is popularly known as the spawn by which the mushroom is frequently propagated. In favorable circumstances this mycelium spreads with great rapidity, sometimes, especially when prevented from developing organs of reproduction, attaining enormous dimensions. It may be kept dormant in a dry state for a long time, ready to grow up into perfect plants when the necessary heat and moisture are applied. When the requisite conditions are present and the mycelium begins to develop the reproductive tissue, there is formed at first a small, round tubercle, in which the rudiments or miniature organs of the future plant may, after a while, be distinctly traced. In this infantile condition, the mushroom is covered completely with a fine, silky veil or volva, which afterward disappears. The tubercle rapidly increases, until at last it produces from its interior a long, thick, fleshy stem, or stipe, surmounted by a pileus, or round convex, concave, or flat cap, similar to that anciently worn by the Scottish peasantry. This is the organ of reproduction, equivalent to the thecæ of mosses and the flowers of phanerogamous plants. This cap is covered with a veil or wrapper, which is ruptured at a certain stage, and retires to form an annulus or ring round the stem. When it is removed from the under side of the pileus, a number of vertical plates or gills is revealed of a pale pinkish-yellow or white color, different from the rest of the plant, and radiating round the cap from a common centre.