If the spore of this Polyporus lodges on a wound which exposes the cambium and young wood, the filaments grow into the medullary rays and the vessels and soon spread in all directions in the timber, especially longitudinally, causing the latter to assume a warm brown color and to undergo decay.  In the infested timber are to observed radial and other crevices filled with the dense felt-like mycelium formed by the common growth of the innumerable branched filaments.  In bad cases it is possible to strip sheets of this yellowish white felt work out of the cracks, and on looking at the timber more closely (of the oak, for instance), the vessels are found to be filled with the fungus filaments, and look like long white streaks in longitudinal sections of the wood—­showing as white dots in transverse sections.

It is not necessary to dwell on the details of the histology of the diseased timber; the ultimate filaments of the fungus penetrate the walls of all the cells and vessels, dissolve and destroy the starch in the medullary rays, and convert the lignified walls of the wood elements back again into cellulose.  This evidently occurs by some solvent action, and is due to a ferment excreted from the fungus filaments, and the destroyed timber becomes reduced to a brown mass of powder.

I cannot leave this subject without referring to a remarkably interesting museum specimen which Prof.  Hartig showed and explained to me last summer.  This is a block of wood containing an enormous irregularly spheroidal mass of the white felted mycelium of this fungus, Polyporus sulphureus.  The mass had been cut clean across, and the section exposed a number of thin brown ovoid bodies embedded in the closely woven felt; these bodies were of the size and shape of acorns, but were simply hollow shells filled with the same felt-like mycelium as that in which they were embedded.  They were cut in all directions, and so appeared as circles in some cases.  These bodies are, in fact, the outer shells of so many acorns, embedded in and hollowed out by the mycelium of Polyporus sulphureus.  Hartig’s ingenious explanation of their presence speaks for itself.  A squirrel had stored up the acorns in a hollow in the timber, and had not returned to them—­what tragedy intervenes must be left to the imagination.  The Polyporus had then invaded the hollow, and the acorns, and had dissolved and destroyed the cellular and starchy contents of the latter, leaving only the cuticularized and corky shells, looking exactly like fossil eggs in the matrix.  I hardly think geology can beat this for a true story.

The three diseases so far described serve very well as types of a number of others known to be due to the invasion of timber and the dissolution of the walls of its cells, fibers, and vessels by hymenomycetous fungi, i.e., by fungi allied to the toadstools and polypores.  They all “rot” the timber by destroying its structure and substance, starting from the cambium and medullary rays.