of old beeches and spruce fir stumps, but they are also to be found in oaks, plums, various conifers, and probably may occur in most of our timber trees if opportunity offers. The most important point in this connection is that _Agaricus melleus_ becomes in these cases a true parasite, producing fatal disease in the attacked timber trees, and, as Hartig has conclusively proved, spreading from one tree to another by means of the rhizomorphs under ground. Only the last summer I had an opportunity of witnessing, on a large scale, the damage that can be done to timber by this fungus. Hundreds of spruce firs with fine tall stems, growing on the hillsides of a valley in the Bavarian Alps, were shown to me as "victims to a kind of rot." In most cases the trees (which at first sight appeared only slightly unhealthy) gave a hollow sound when struck, and the foresters told me that nearly every tree was rotten at the core. I had found the mycelium of _Agaricus melleus_ in the rotting stumps of previously felled trees all up and down the same valley, but it was not satisfactory to simply assume that the "rot" was the same in both cases, though the foresters assured me it was so. [Illustration: FIG. 15.--A small group of _Agaricus (Armillaria) melleus_. The toadstool is tawny yellow, and produces white spores; the gills are decurrent, and the stem bears a ring. The fine hair-like appendages on the pileus should be bolder.] By the kindness of the forest manager I was allowed to fell one of these trees. It was chosen at hazard, after the men had struck a large number, to show me how easily the hollow trees could be detected by the sound. The tree was felled by sawing close to the roots; the interior was hollow for several feet up the stem, and two of the main roots were hollow as far as we could poke canes, and no doubt further. The dark-colored rotting mass around the hollow was wet and spongy, and consisted of disintegrated wood held together by a mesh work of the rhizomorphs. Further outward the wood was yellow, with white patches scattered in the yellow matrix, and, again, the rhizomorph strands were seen running in all directions through the mass. [Illustration: FIG. 16.--Sketch of the base of a young tree (s) killed by _Agaricus melleus_, which has attacked the roots, and developed rhizomorphs at r, and fructifications. To the right the fructifications have been traced by dissection to the rhizomorph strands which produced them.] Not to follow this particular case further--since we are concerned with the general features of the diseases of timber--I may pass to the consideration of the diagnosis of this disease caused by _Agaricus melleus_, as contrasted with that due to _Trametes radiciperda_.