CANKER AND DRY-ROT. 75 



up ; while resin flows out at the wound in the bark, which en- 

 larges yearly as the tissues surround it with successively wider- 

 gaping lips of cork in the futile effort of the tree's vitality to heal 

 it over. Round the margins of the wound appear the little 

 orange cup-shaped fructifications of the Peziza scattering their 

 spores so as to infect other trees ; whilst the ultimate effect is 

 that each tree is ringed by the destruction of its cortex and then 

 generally succumbs. 



Many of the fungi which attack standing timber are so ruinous 

 in their action that the wood of the affected trees will never 

 reach the hands of the timber-merchant; but the wood worker is 

 more seriously interested in those diseases which attack converted 

 timber. Of these the most important is "dry rot" (Merulius 

 Idcrymans). The spores of this fungus germinate on damp wood, 

 provided some alkali is present, such as the ammonia fumes in 

 stables. Then, under the influence of warm, still air (i.e. the 

 absence of ventilation) its spawn-threads spread not only in all 

 directions through the wood, forming greyish-white cords and 

 flat cake-like masses of felt on its surface, but even over surfaces 

 of damp soil or brickwork, and thus to other previously unin- 

 fected timbers. Feeding upon the elements of the wood, getting 

 its nitrogen from cells which retain their protoplasm, such as 

 those of the pith-rays, but its carbonaceous and mineral sub- 

 stances from the walls of the tracheids and other fibrous elements, 

 the fungus destroys the substance of the timber, lessening its 

 weight, and causing it to warp and crack; until, at length, it- 

 crumbles up when dry into a fine brown powder, or, readily 

 absorbing any moisture in its neighbourhood, becomes a soft, 

 cheese like mass. At an earlier stage the affected timber appears 

 dark-coloured and dull ; and, long before its total disorganization, 

 it will have lost most of its strength. Imperfectly seasoned 

 timber is most susceptible to dry rot : the fungus can be spread 

 either by its spawn or by spores, and these latter can be carried 

 even by the clothes or saws of workmen, and are, of course, only 

 too likely to reach sound wood if diseased timber is left about 

 near it ; but on the other hand dry timber kept dry is proof 



