154 TIMBER AND SOME OF ITS DISEASES. [CH. v. 



lamella between the contiguous elements of the wood 

 subsequently dissolves, and soft places and cavities 

 are produced, causing the previously firm timber to 

 become spongy and soft, and it eventually breaks 

 up into a rotting mass of vegetable remains. 



It will readily be understood that all these pro- 

 gressive changes are accompanied by a decrease in 

 the specific gravity of the timber, for the fungus de- 

 composes the substance much in the same way as it 

 is decomposed by putrefaction or combustion, i£. it 

 causes the burning off of the carbon, hydrogen, and 

 nitrogen, in the presence of oxygen, to carbon-dioxide, 

 water, and ammonia, retaining part in its own sub- 

 stance for the time being, and living at its expense. 



