Page:Popular Science Monthly Volume 15.djvu/547

Rh with the seeds of decay, stimulated by moisture, the bad atmosphere of an ill-contrived burial-place, and afterward by heat from the stoves constantly in use. All these circumstances account satisfactorily for the extraordinary and rapid growth of the fungi.

The decayed state of a barn-floor attacked by rot is thus described by Mr. B. Johnson: "An oak barn-floor which had been laid twelve years began to shake upon the joists, and on examination was found to be quite rotten in various parts. The planks, two and a half inches in thickness, were nearly eaten through, except the outsides, which were glossy and without blemish. The rotten wood was partly in a state of snuff-colored, impalpable powder; other parts were black, and the rest clearly fungus. No earth was near the wood."

An indication of dry-rot in a damp pantry will be a coating of fine powder, like brick-dust, upon the shelves and earthenware, which consists of myriads of reddish spores shed by the dry-rot fungus. When these spores fall upon a wet surface, the red skin cracks at both ends, and fine filaments are sent out, which grow and ramify in all directions, and do their work of mischief with the timber of the closet.

Ventilation as a remedy for dry-rot in buildings is of doubtful service. If dry air be admitted in such a way as to absorb the moisture which sustains it, the fungus will of course be destroyed; but the trouble is that the circulating air will carry the spores along with it, and so spread the disease to unaffected parts. This is the great danger with dry-rot, while the wet-rot or ordinary decay is only communicated by actual contact. Another difficulty in ventilating for dry-rot arises from the fact that air, in passing through damp places, soon becomes humid, and loses its efficacy, or even does more harm than good. Intestinal decay is not reached by ventilation, for the air can not penetrate the spongeous exterior rottenness of timber so affected.

The temperature at which dry-rot proceeds most rapidly is 80° Fahr. At 90° it is slower, and at 100° slower still, and from 110° to 120° is generally arrested. Its progress is rapid at 50°, slow at 36°, and is arrested at 32°; but will return if the temperature is again raised to 50°. But in a constancy and equality of temperature timber will endure for ages. The wooden piles on which Venice and Amsterdam are founded remain sound because of the constancy of the conditions that surround them. Nothing is more destructive to wood than partial wetting. If it be kept always wet or always dry, and at a steady temperature, decay does not begin. It is recorded that a pile was drawn up sound from a bridge on the Danube that parted the Austrian and Turkish dominions, which had been under water fifteen hundred years. It has been remarked that the part of a ship which is constantly washed by bilge-water is never affected by dry-rot; and that the planking of a ship's bottom which is next the water remains sound for a long time, even when the inside is quite rotten.

As the decay of wood is chiefly due to the presence in it of sap, and