INTRODUCTION. 7 



with others of its kind; the pith-ray; the resin-duct, and others, 

 all of which are often popularly referred to as fibres. 



The character and the arrangement of cell-structures differ 

 with species. Wood is hard, soft, light, heavy, tough, porous, 

 elastic, or othenvise, because of these differences. Appearance 

 is affected, and woods may be distinguished from one another, 

 because of this fact. 



The character of wood not only depends upon the properties 

 and the arrangement of the cell structures, but it also depends 

 upon the characteristics and the quantities of substances asso- 

 ciated with, although actually foreign to, the cell structures. 

 Sap or pure water is thus within although not readily part of the 

 wood tissue. Water distends and weakens cell structures which 

 are then more pliable. 



Most wood is used in "construction," that is, in mines, 

 railways, houses and ships, where demand is for size or 

 quantity, and where finish and appearance amount to but little. 

 Much wood is used in decoration and furniture, where appear- 

 ance, appropriateness, and finish are called for; but these 

 woods, although much in evidence, are infinitely less in quantity 

 than those employed in construction. Some wood is required 

 for implements, turnery, carvings and small-piece work, where 

 size is secondary and where qualities such as hardness, fine 

 grain, and uniformity, controllable in small pieces, are primary. 

 Some wood is used indirectly, as in the manufacture of 

 paper-pulp, gunpowder and chemicals. There are also by- 

 products of trees, such as tanbark, turpentine, resin, nuts and 

 sugar. 



The weight, strength, and other measurable properties of 

 wood are variable. Weight varies from day to day as water 

 is absorbed and evaporated. Strength differs with grain, age, 

 moisture, specific gravity, and many other things. Two pieces 

 from different portions of the same tree differ from each other. 

 The proportions of sap and heart wood are seldom constant. 

 Results from small specimens may differ from those obtained 



