FLEXIBILITT AND BLABTIOITT. 15 



Section IV. — Flexibility and Elasticity. 



We understand by flexibility the capability of being bent out 

 of sbape without any kind of rupture of the component wood 

 elements. Elasticity in addition to flexibility implies a return, 

 more or less complete, to the original shape, that is to say, the 

 resumption of their original relative positions by the elements. 

 Thus mere flexibility and elasticity, although closely inter-connected 

 up to a certain point, are difi^erent properties. Both agree in re- 

 quiring the fibres to be more or less extensible and to play upon 

 one another ; and for this reason they both require the fibres to be 

 long and straight and parallel, and the wood to be homogeneous. 

 In the case of woods with distinct concentric rings, both properties 

 are heightened by narrowness of the rings, which form thin plates 

 capable of moving one upon another like the leaves of a book. 



Flexibility. — Mere flexibility without elasticity is favoured by 

 a wet condition of the fibres, the walls of which are then soft enough 

 to stretch and change shape easily. Hence steaming under a high 

 pressure, or which nearly comes to the same thing, exposure in a 

 green state to a temperature sufficient to form steam, gives wood 

 its maximum of flexibility. As a rule, light woods are more 

 flexible than heavy woods, because their looser structure gives more 

 room for the play of the fibres upon one another, and enable them 

 to become soaked with moisture more easily and completely. Hence 

 the wood of the roots is more flexible than that of the stem, which 

 itself is, with few exceptions, more flexible than that of the branches. 

 For the same reason, and also because it contains more moisture, 

 sapwood is more flexible than heartwood, and the outer concentric 

 rings than those further in the interior. The wood of trees grown in 

 wet soils is often more pliable than the wood of trees grown on 

 dry soils; For one and the same species young stool-shoots are 

 more flexible than seedlings of the same size. The wood of clim- 

 bers is the most flexible of all, being very straight and long-fibred 

 and of loose texture. 



Flexible wood is used for band boxes, drums, frames for sieves, 

 hoops, wicker work, matting (bamboos and canes), wattling, withies, 

 bentwood furniture, &c. Wood that has been made flexible arti- 

 flcially, loses all its flexibility and becomes very brittle, once it is 

 dry. 



Elasticity. — Moisture diminishes elasticity, only dry (but not 

 too dry) or moderately green wood being elastic. For one and 

 the same species weight always increases elasticity. Hence well- 

 nourished wood is more elastic than wood of loose texture, the 



