rhizomorphs may also be found spreading around into the soil from the roots, and they look so much like thin roots indeed that we can at once understand their name—­rhizomorph.  The presence of the rhizomorphs and (in the case of the resinous pines) the outflow of resin and sticking together of soil and roots are good distinctive features.  No less evident are the differences to be found on examining the diseased timber, as exemplified by Prof.  Hartig’s magnificent specimens.  The wood attacked assumes brown and bright yellow colors, and is marked by sharp brown or nearly black lines, bounding areas of one color and separating them from areas of another color.  In some cases the yellow color is quite bright—­canary yellow, or nearly so.  The white areas scattered in this yellow matrix have no black specks in them, and can thus be distinguished from those due to the Trametes.  In advanced stages the purple-black rhizomorphs will be found in the soft, spongy wood.

The great danger of Agaricus melleus is its power of extending itself beneath the soil by means of the spreading rhizomorphs; these are known to reach lengths of several feet, and to pass from root to root, keeping a more or less horizontal course at a depth of six or eight inches or so in the ground.  On reaching the root of another tree, the tips of the branched rhizomorph penetrate the living cortex, and grow forward in the plane of the cambium, sending off smaller ramifications into the medullary rays and (in the case of the pines, etc.) into the resin passages.  The hyphae of the ultimate twigs enter the tracheides, vessels, etc., of the wood, and delignify them, with changes of color and substance as described.  Reference must be made to Prof.  Hartig’s publications for the details which serve to distinguish histologically between timber attacked by Agaricus melleus and by Trametes or other fungi.  Enough has been said to show that diagnosis is possible, and indeed to an expert not difficult.

It is at least clear from the above sketch that we can distinguish these two kinds of diseases of timber, and it will be seen on reflection that this depends on knowledge of the structure and functions of the timber and cambium on the one hand and proper acquaintance with the biology of the fungi on the other.  It is the victory of the fungus over the timber in the struggle for existence which brings about the disease; and one who is ignorant of these points will be apt to go astray in any reasoning which concerns the whole question.  Any one knowing the facts and understanding their bearings, on the contrary, possesses the key to a reasonable treatment of the timber; and this is important, because the two diseases referred to can be eradicated from young plantations and the areas of their ravages limited in older forests.