PLIABILITY. 43 



wood elastic, but may altogether nullify its flexibility. Damp 

 and heat combined render a wood very flexible, but never 

 increase its elasticity ; so, when completely saturated with water, 

 the elasticity of a wood is quite thrown into the background by 

 the surprising increase of its flexibility. Basket-work by means 

 of finely-split ribbons of wood of aspens, sallows and spruce, is 

 an example of this treatment. 



Another factor is the resin of conifers. According to Nord- 

 linger, a certain amount of resin, as it occurs in the heartwood 

 of Scotch pine and larch, increases the elasticity of a wood, 

 while too much resin renders a wood brittle. 



Frost reduces both the elasticity and flexibility of wood. 

 Girdling living trees and allowing them to die standing increases 

 the flexibility of their wood. 



Much more observation is required before a satisfactory 

 detailed knowledge of the elasticity and flexibility of woods has 

 been acquired, scientific observation having hitherto established 

 certain facts regarding these properties which are quite at variance 

 with popular ideas of the subject. The question will now be 

 dealt with separately under the headings elasticity and 

 flexibility. 



2. Elasticity. 



Two factors appear to be chiefly influential in determining the 

 elasticity of a wood. They are its specific gravity and anatomical 

 structure. The heaviest European woods are usually the most 

 elastic — as, for instance, yew, robinia, oak, sycamore and ash ; for 

 the elastic masts of ships, only narrow-ringed, heavy Scotch 

 pine-wood is suitable. The heavier stemwood of trees is more 

 elastic than the lighter rootwood. 



As regards anatomical structure, even grain (uniformly-sized 

 fibres), long and parallel wood-fibres, and freedom from branches, 

 knots and other abnormities, increase the elasticity of a 

 wood. This explains the elasticity of certain woods with low 

 specific gravity, as, for instance, spruce, silver-fir, larch, Scotch 

 pine and lime-wood. These woods also, when narrow-zoned, and 

 consequently heavier, are more elastic than when more rapidly 

 grown and consequently softer. 



Sprucewood is generally used for sounding-boards to musical 



