60 OF WOOD IN GENERAL 



of moisture, air, and some degree of heat, exert a solvent action, 

 some on cellulose, some on lignin. The fungus feeds on what it 

 dissolves, and specially flourishes in the living nitrogenous matter 

 of sapwood. As no fungal growth takes place without water and 

 air, neither absolutely dry wood, nor completely submerged wood, 

 will decay. Some fungi confine their attacks to Hving trees, others 

 to timber after it is felled ; and of the first-mentioned class some 

 are true 'parasites, attacking the roots of Hving and otherwise 

 healthy trees, whilst others are wound-parasites, the minute spores 

 or reproductive germs finding their way into the tree through 

 some woxmd not produced by the fungus. Holes bored by insects, 

 excoriations of the bark by animals of any kind, and branches 

 broken by wind or badly pruned, afford wounds suitable for the 

 attacks of these last. When the disease caused by a wound-para- 

 site manifests itself first in the cortical and cambium tissues it is 

 termed a canker. Some fungi are confined to single species of trees, 

 others attack conifers only, others hard woods only, whilst some 

 seem capable of attacking trees of all kinds ahke. The fungi most 

 destructive to timber belong to the more highly organized sub- 

 divisions of the class, the Peziza, which produces the canker in the 

 Larch, being, for instance, one of the Ascomycetes, whilst many 

 others known as " wet rot," " dry rot," etc., are members of the 

 order Eymenomy cites, that to which the mushrooms belong. 



One of the most generally destructive of these last is the toad- 

 stool Agdricus {Armilldria) melleus, clusters of the yellow fructi- 

 fications of which are often seen near the base of unhealthy Beech, 

 Spruce, Oak, or other trees in autumn. The upper surface of its 

 tawny cap is shaggy with hair ; the gills on the under surface run 

 down on to the stalk, round which there is a well-marked torn 

 ring ; and the spores, when ripe, are white. Underground, instead 

 of the dehcate white " spawn " or mycehum, resembling cobweb, 

 which is common among fungi, this species produces stout, pur- 

 plish-black strands, which may extend, at a depth of six or eight 

 inches below the surface, to a distance of several feet. These strands 

 are known as rhizomorphs, from their root-hke appearance. They 

 have growing points capable of penetrating the cortex of living tree 

 roots, and, when they have done so, extend into the cambium and 

 send off branches into the pith-rays and the wood. When this 

 parasite attacks a resinous tree, such as Spruce, a quantity^ of the 

 resin flows from the pierced root, and the fungal threads * travel 

 partly along the resin-passages. In these cases the fungal threads 

 commonly exude a fermentative secretion, by means of which they 

 soften and dissolve the walls of cells or vessels : on penetrating cells 

 containing protoplasm, starch, etc., they readily absorb such 



