72 OF WOOD IN GENERAL. 



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- 

 parasite 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 alike. 

 The fungi most destructive to timber belong to the more highly 

 organized subdivisions of the class, the Peziza, which produces the 

 canker in the Larch, being, for instance, one of the Ascomyc6tes, 

 whilst many others known as " wet rot," " dry rot," etc., are 

 members of the order Hymenomycttes, that to which the mushrooms 

 belong. 



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

 stool Agdricus (Armilldria) malleus, 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 delicate white " spawn " or mycelium, resembling cobweb, 

 which is common among fungi, this species produces stout, 

 purplish-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-like 

 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 substances ; but they also destroy 

 cellulose and lignin itself, at first producing various discolorations 



