DRY ROT. A disease which attacks wood, rendering it brittle, and destroy ing the cohesion of its parts, is known by this name. It occurs among the tim bers of ships, where it sometimes com mits the most serious damage,' Ind in damp ill-ventilated houses. It is usually ascribed to the attacks of fungi, espe cially to such as Polyporus destructor and jferuliue lachryrnane, whose filamen tous spawn or thallus appears upon the surface, overspreading it like a tough thick skin of white leather ; and there is no doubt of its being often connected with appearance of such fungi. But dry rot is certainly, in some cases, to be identi fied with the presence of a fungi of a more simple kind than those just men tioned; especially of such as belong to or resemble the genus Sporotrichum.
The destruction of timber by such plants is effected in part by the disin tegration of the tubes of the weed, in consequence of the introduction between them of the fine filamentous spawn of the fungi, and in part by the dampness which is thus conveyed to the interior of the wood, where it soon produces de composition. It is not, however, certain that dry rot is always caused in this manner ; on the contrary, the term ap pears to be frequently applied to cases of spontaneous decomposition of timber without the presence of fungi, or when the appearance of the latter takes place long after the commencement of the dis ease.
When dry rot produced by fungi has once made its appearance, there is no means of arresting its progress without removing the whole of the diseased and neighboring parts ; and even then it will probably again break out, unless means can be taken to introduce a circulation of fresh air among the parts liable to the affection. For if timber is allowed to
remain in a damp situation, and in the dark, it affords so favorable a nidus for the seeds of fungi, that they are almost certain to vegetate upon it ; unless some means have been previously taken to render the timber permanently unsuited to their growth. This end appears to have been attained by Mr. Ryan, who obtained a patent for pickling timber, as a preventive of the dry rot, and who employed for this purpose a solution of corrosive sublimate. This salt of mer cury is a well-known vegetable poison : if any animal jelly, upon which fungi will quickly appear in the form of mouldi ness, is mixed with a minute quantity of corrosive sublimate, no fungi will in that case be produced ; so that both theory and experience are in favor of Mr. Kv an's process. It is not improbable that the progress of dry rot might even be arrested in the buildings where it occurs, if the timbers could be got at and well washed with the same solution.
Although dry rot generally fixes itself upon timber, it will also attack any form of vegetable matter. The paper hang ings of rooms, chiefly composed of cot ton and linen thread, are occasionally overrun in houses which have been long shut up and neglected; and the mildew which destroys the strength of canvas is only another form of dry rot, the ap pearance of which is altered by the special circumstances under which the fungus is developed, or by the species of the fun gus itself. (See PRESERVATION Or.)