AMERICAN FOREST TREES 15 



attacked at once, and before cold weather stops the activities of fungus 

 it has reached the interior of the wood and the process of rotting is 

 under way. When the agents of decay have begun to grow in the wood, 

 destruction will go on as long as air and moisture conditions are favor- 

 able. 



The bluing of wood is an incipient decay and is generally due to 

 fungus. Some kinds of wood are more susceptible to bluing than others. 

 Though boards may quickly season sufficiently to put a stop to the bluing 

 process before it has actually weakened the material, the result is more 

 or less injurious. The wood's natural color and luster undergo deteri- 

 oration ; it does not reflect light as formerly, and seems dead and flat. 



Decay affects sapwood more readily than heart. The reason may 

 be that sapwood contains more food for fungus, thereby inducing greater 

 activity. The sapwood is on the outside of timbers and is often more 

 exposed than the heart. In some instances greater decay may be due to 

 greater exposure. Another reason for more rapid decay of sapwood 

 than heart is the fact that the pores of the heartwood are more or less 

 filled with coloring matter deposited while the growth of the tree was 

 in progress. The coloring matter, in many cases, acts as a preservative ; 

 it shuts the threads of fungus out. Sometimes the sapwood of a dead 

 tree or a log is totally destroyed while the heart remains sound. This 

 often happens with red cedar and sometimes with black walnut, yellow 

 poplar, and cherry. Occasionally a tree's bark is more resistant to decay 

 than its wood. Paper birch and yellow birch logs in damp situa- 

 tions occasionally show this. What appears to be a solid fallen trunk, 

 proves to be nothing more than a shell of bark with a soft, pulpy 

 mass of decayed wood within. 



