We may thus see how much art feeling the architects of these remote epochs possessed, and express our wonder at the extreme taste that presided over all these marvelous subterranean structures.—­A.  Tissandier, in La Nature.

* * * * *

[NATURE.]

TIMBER, AND SOME OF ITS DISEASES.[1]

   [Footnote 1:  Continued from SUPPLEMENT, No, 640, p. 10222.]

By H. MARSHALL WARD.

IV.

Before proceeding further it will be of advantage to describe another tree-killing fungus, which has long been well known to mycologists as one of the commonest of our toadstools growing from rotten stumps and decaying wood-work such as old water pipes, bridges, etc.  This is Agaricus melleus (Fig. 15), a tawny yellow toadstool with a ring round its stem, and its gills running down on the stem and bearing white spores, and which springs in tufts from the base of dead and dying trees during September and October.  It is very common in this country, and I have often found it on beeches and other trees in Surrey, but it has been regarded as simply springing from the dead rotten wood, etc., at the base of the tree.  As a matter of fact, however, this toadstool is traced to a series of dark shining strings, looking almost like the purple-black leaf stalks of the maidenhair fern, and these strings branch and meander in the wood of the tree, and in the soil, and may attain even great lengths—­several feet, for instance.  The interest of all this is enhanced when we know that until the last few years these long black cords were supposed to be a peculiar form of fungus, and were known as Rhizomorpha.  They are, however, the subterranean vegetative parts (mycelium) of the agaric we are concerned with, and they can be traced without break of continuity from the base of the toadstool into the soil and tree (Fig. 16).  I have several times followed these dark mycelial cords into the timber 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.