54 WOOD AND FOREST. 



Stiffness is the ability to resist bending, and hence is the opposite 

 of pliability or flexibility. A wood may be both stiff and elastic; it 

 may be even stiff and pliable, as ash, which may be made into splints 

 for baskets and may also be used for oars. Willow sprouts are flexible 

 when green, but quite brittle when dry. 



Elasticity is of great importance in some uses of wood, as in long 

 tool handles used in agricultural implements, such as rakes, hoes, 

 scythes, and in axes, in archery bows, in golf sticks, etc., in all of 

 which, hickory, our most elastic wood, is used. 8 



HARDNESS OF WOOD. 



Hardness is the ability of wood to resist indentations, and de- 

 pends primarily upon the thickness of the cell walls and the small- 

 ness of the cell cavities, or, in general, upon the density of the wood 

 structure. Summer wood, as we have seen, is much harder than 

 spring wood, hence it is important in using such wood as yellow pine 

 on floors to use comb-grain boards, so as to present the softer spring 

 wood in as narrow surfaces as possible. See Handwork in Wood, 

 p. 41, and Fig. 55. In slash-grain boards, broad surfaces of both 

 spring and summer wood appear. Maple which is uniformly hard 

 makes the best floors, even better than oak, parts of which are com- 

 paratively soft. 



The hardness of wood is of much consequence in gluing pieces to- 

 gether. Soft woods, like pine, can be glued easily, because the fibers 

 can be forced close together. As a matter of fact, the joint when dry 

 is stronger than the rest of the board. In gluing hard woods, how- 

 ever, it is necessary to scratch the surfaces to be glued in order to 

 insure a strong joint. It is for the same reason that a joint made 

 with liquid glue is safe on soft wood when it would be weak on 

 hard wood. 9 



TOUGHNESS OF WOOD. 



Toughness may be defined as the ability to resist sudden shocks 

 and blows. This requires a combination of various qualities, strength, 

 hardness, elasticity and pliability. The tough woods, par excellence, 



8 For table of elasticity of different woods, see Sargent, Jesup Collection, 

 pp. 163 ff. 



"For table of hardnesses of different woods, see Sargent, Jesup Collec- 

 tion, pp. 173 ff. 



