88 Trees, Stars, and Birds 



(Durability of woods. Decay in wood is caused by 

 fungi. These are small plants that grow in the wood 

 and use it as food. Some woods have in them resins, 

 gums, oils, turpentine, coloring matter, and other sub- 

 stances that prevent the growth of fungi in them. Such 

 woods are very durable, and in buildings in China and 

 in Europe wood that has lasted for many centuries 

 may be found. Yellow pine is valuable for porch floors, 

 because the wood is protected by resin in the boards. 



Why are houses painted? If a house is not painted 

 until decay has started in the wood, will the decay con- 

 tinue after the painting is done? If the timbers used 

 in the walls of a house are partly decayed when the 

 house is built, will the decay continue after the house 

 is completed? Will decay spread from one board to 

 another if the two are placed in contact? Does a post 

 decay more quickly in the air, at the surface of the 

 ground, or when buried deep in the ground? Does 

 wood that is immersed deep in water decay? Why 

 and how are railroad ties creosoted? 



The durability of woods is affected also by the amount 

 of moisture they contain, and probably also by the 

 structure of the wood and the amount of food stored in 

 it. Generally speaking, wood from a tree that has 

 grown slowly in a forest is more durable than wood from 

 a tree that has grown rapidly in the open, and in many 

 species of trees the heartwood is more durable than the 

 sap wood. 



Name some kinds of wood that decay in a few years. 

 What kinds are more durable? Name several ways of 

 treating wood to make it last. 



