Page:Popular Science Monthly Volume 15.djvu/543

Rh the mold on which this singular plant is seen to grow, you will find it penetrated with delicate, whitish, interlacing filaments which are the vegetative system of the plant. This part of a mushroom is called the mycelium, and from it arises the reproductive portion which grows above ground. But the only part of this above-ground portion that is essential, and that is found in all fungi whatever, is just that part which escapes ordinary observation. Everybody has seen the umbrella-like cap with the radiating vertical plates on its under surface. These plates are covered by a membrane which has the same office as the seed-vessel of the higher plants. It bears the minute reproductive bodies of the fungi, analogous to common seeds, and called spores.

The only parts of a mushroom which are common to all fungi are the mycelium or thready, interlacing portion which grows underground, and the minute, microscopic spores which are cellular in structure and so small that thousands of them are required to form a body the size of a pin's head. The fungi differ among themselves in many ways; but mycelia and spore production always occur in them, and are their essential characters. Every plant of which this mycelium forms a part, spreading its web throughout the substance on, or in, which it grows, belongs among fungi. Most of the species are either quite invisible, or else their parts are so small as to be indistinguishable. But some sort of reproductive organs exist, and spores are always produced. The mycelium is often so minute as to traverse living plants and the pores of solid wood. It grows rapidly and causes quick decay. Potato-rot, the yeast-and vinegar-plants, mildews, rusts, and smuts of grain, and molds of all kinds, are part of this immense group of plants that lives upon decay and fills the air with its countless myriads of spores. These subtile, germinal particles are lodged everywhere. They are light as vapor and abound in air, in water, in dust, in sand, ready, when warmth and moisture favor, to burst into life. As has been said, the dry-rot fungi flourish upon the products of wet-rot. Different stages of decay produce food of different qualities, adapted to different species of fungi. One species takes up the process where another leaves it, and carries it further and further forward.

Dry-rot may begin its ravages in the interior of timber as easily as upon the surface. As atmospheric dust is filled with the spores of fungi, they may be conveyed by rain into the earth, absorbed by the roots of vegetables, and diffused with the sap throughout the whole plant. There are numerous species of dry-rot fungi adapted to different conditions of life and presenting different aspects. Nor are they restricted to timber. They may flourish in the earth, where they present a perfectly white mycelium, branching and interlacing like roots; and when workmen are employed on grounds which are affected by the dry-rot fungi their health is often disturbed. A few years since, while a London builder was putting up some houses at Hampstead, his men were never well. He afterward learned that the ground was affected