178 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



looks as if it had been burnt or scorched on the injured 

 side. If the beam or plank is wet, the diseased parts 

 are found to be so soft that they can easily be cut with 

 a knife, almost like cheese ; when dry, however, the 

 touch of a hard instrument breaks the wood into brittle 

 fibrous bits, easily crushed between the fingers to a 

 yellow-brown, snuff-like powder. The timber has by 

 this time lost its coherence, which, as we have seen, 

 depends on the firm interlocking and holding together 

 of the uninjured fibrous elements, and may give way 

 under even light loads a fact only too well known to 

 builders and tenants. The walls of the wood-elements 

 (tracheides, vessels, fibres, or cells, according to the 

 kind of timber, and the part affected) are now, in fact, 

 reduced more or less to powder, and if such badly 

 diseased timber is placed in water it rapidly absorbs 

 it and sinks : the wood in this condition also readily 

 condenses and absorbs moisture from damp air, a fact 

 which we shall see has an important bearing on the 

 progress of the disease itself. 



If such a piece of badly diseased deal as I have 

 shortly described is carefully examined, the observer 

 is easily convinced that fungus filaments (mycelium) 

 are present in the timber, and the microscope shows 

 that the finer filaments of the mycelium (hyphae) are 

 permeating the rotting timber in all directions run- 



