2'60 FIKST BOOK OF FUlJESTKY 



Some Chemical Properties 



When sufficiently heated wood burns or oxidizes ; and 

 this, while it is not a desirable quality in a building mate- 

 rial, is otherwise one of its greatest virtues. 



If lieated in a close vessel, various substances are made 

 in the form of gases ; and, as we have seen, this is taken 

 advantage of by the '• acid man.'" 



By means of chemicals wood is easily changed into 

 sugar ; and if ever this can be done cheaply enough, wood 

 may become an important source of food. 



Durability and Decaij. — All kinds of wood are subject 

 to destruction by decay-producing fungi. One of the 

 countless millions of spores of some fungus drops on a 

 timber, and is carried by a raindrop into the interior of 

 a pore. If conditions are favorable, it genninates, grows 

 into a thread of " mycelium "; and this thread, which is a 

 series of living cells, attaches itself closely to the wall of 

 the wood cell, secretes a juice which is capable of dissolv- 

 ing wood, and which changes at least a part of it into 

 sugarlike substances which are taken into the cells of the 

 mycelium as food. Now decay has begun, and in a short 

 time, if beech or maple is the timber, it is penetrated in 

 all directions. At first the wood is merely discolored, and 

 looks " dead " ; later on it becomes brittle, and finally 

 it becomes a powdery mass, and in keeping with these 

 changes loses its resistance. 



