J 



an. 12, 



1 888] 



NA TURE 



2^1 



the north and by about 2" in tlie south, and, like the lines 

 of horizontal component, the isoclinals have not been 

 displaced parallel to themselves, but in a direction 

 approximating to that of the parallels of latitude. The 

 secular change is least in the north east and gradually 

 ncreases towards the south, and attains its maximum 

 dong the Pyrenees and towards the Gulf cf Genoa. 



M. iMoureaux is to be congratulate ;l on the results of his 

 work, for his countrymen have hitherto scarcely contributed 

 their fair share to our knowledge of terrestrial magnetism. 

 Even the surveys of their own country have been made 

 for them by Germans and Englishmen. Now that 

 Frenchmen themselves have made a beginning, it is to 

 be hoped that the continuity of the work will not be 

 interrupted, for it is only by systematic survey work of 

 the kind so successfully accomplished by AI. iMoureaux 

 that our knowledge of the magnetic state of the earth and 

 )f the laws which regulate its cha-iges can be elucidated. 



T. E. Thorpe. 



TIMBER, AND SOME OF ITS DISEASES} 



IV. 



T) EFORE proceeding further it v/ill be of advantage to 

 -L' describe another tree-killing fungus, which has long 

 been well known to mycologists as one of the commonest ot 

 our toadstools growing from rotten stumps, and decaying 

 wood-work such as old water-pipes, bridges, &c. This is 

 A^arkies melleiis (Fig. 15), a tawny yellow toadstool with 



KiG. 15 — A small group of A ;a'iiiis {Ar./tillaria.) vielleus. The toad-stool 

 is tawny-yell )w, and proiuc:s white spores; the gills are decurrent, 

 and the stem b^ari a ring. The fine ha'.r-Iik; append iges on the pileus 

 should be bolder. 



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 

 CortI;iiied f.om p. 229. 



\ have often found it on beeches and other trees in 

 Surrey, but it has been regarded as simply springing from 

 the dead rotten wood, &c., 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 wo 

 know that until the last {(t\\ years these long black cords 

 were supposed to be a peculiar form of fungus, and were 

 known as Rhizoniorpha. They are, however, the subter- 

 ranean vegetative parts (mycelium) of the Agaric we are 

 concerned v/ith, 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. 



Th2 most important point in this connection is that 

 Agarlcus inelleus becomes in these cases a true parasite, 



Fig. 16.— Sketch of the base of a young tree (jr), killed by Agarlcris iitelieus, 

 which has attacked the roots, and devel )ped rhizomorphs at r, and 

 f/uctificatiins. To t!ie right the f/uctifications have been traced by 

 dissection to the rhizomorph stranJs which produced them. 



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 underground. 

 Only this 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 hill sides 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 Agarlcus Jiielleus 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. 



By the kindness of tlie 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. 



