192 FARM FORESTRY 



reason. Strong woods are usually hard woods, and soft 

 woods do not have much strength. Heavy wood is harder 

 than light wood, especially is this true in the same kind of 

 wood. The wood of the butt log is harder than that of the 

 upper logs, the dark summer wood of the annual ring is 

 harder than the light colored spring wood. 



Durability. Different kinds of woods vary in their dura- 

 bility or the resistance offered to decay when subjected to 

 moist conditions. The question of the durability of woods 

 is of importance to farmers because of the necessity of using 

 woods in contact with the soil, as for posts, poles, stakes, 

 sills, for silos and other purposes. Some woods are very 

 durable while other woods soon decay when kept moist. Just 

 what makes one wood more durable than another is not 

 known. It is believed that during the change from sapwood 

 to heartwood certain tannins, gums and resins are deposited 

 in the walls of the cells along with coloring material which 

 tend to preserve the wood. It may be that more of these 

 substances are deposited in some wood than in others, or that 

 these substances vary in kind. As a general rule dark colored 

 woods are the more durable, as black walnut, mahogany, red 

 wood, red cedar and locust. Light colored woods are usually 

 perishable, like cottonwood, willow, birch and sycamore. Out- 

 side of this fact there seems to be but little relation between 

 the physical properties of different woods and their dura- 

 bility. For example, it might be imagined that heavy woods 

 would be more durable than light woods, but hickory and hard 

 maple, two of our heaviest hardwoods, are not durable, while 

 catalpa and cedar, two of our lightest woods in weight, are 

 very durable. Neither are all soft woods perishable, for cedar, 

 redwood and catalpa are all soft woods. With the same kind 

 of wood, however, the heavier and harder the wood the more 

 durable it will be. That is, a heavy piece of pine is more 

 durable than a light piece. 



The time of year when a tree is cut is often said to have 



