PART II. MATERIALS OF CONSTRUCTION 



CHAPTER VII 



WOOD 



Wood has been the universal material of construction on 

 the farm, and it will be extensively used for a long time in 

 the future, although it is being replaced by clay products, 

 concrete, and concrete and steel. 



Source of supply. Wood suitable for building purposes 

 is of two kinds: soft and hard. It is obtained from the 

 bodies of two classes of trees known as conifers and broad- 

 leaved. The conifers have needlelike leaves, are cone- 

 bearing, usually evergreen, and furnish the greater part 

 of the soft-wood lumber. Trees of this type are the white 

 pine, Norway pine, fir, spruce, redwood, cedar, cypress, 

 hemlock, and others. The broad-leaved trees are usually 

 deciduous and nut-bearing and produce hard wood. Trees 

 of this type are the oak, hard maple, hickory, walnut, ash, 

 elm, beech, gum, and various others. Both conifers and 

 broad-leaved trees are pretty generally distributed over the 

 timbered areas of the United States. It must not be under- 

 stood that a tree can be classified as soft or hard simply 

 from the shape of its leaves or the fact that it is or is not an 

 evergreen. Tamarack is a conifer, deciduous, and produces 

 soft wood; the southern pine is a conifer, evergreen, and 

 produces hard wood; the poplar is broad-leaved, deciduous, 

 and produces soft wood; and the live oak is broad-leaved, 

 evergreen, and produces hard wood. 



Tree growth. Trees which produce lumber grow from 

 the pith or heart outward in a series of concentric rings 

 (Fig. 1 08). Each ring represents one year's growth; the light 

 inner part is soft and weak and represents the spring growth ; 



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