96 PROPERTIES OF WOOD. 



tougher is the wood, and toughness has already been taken 

 into account in the discussion regarding the strength of 

 wood. In practice an unpliable wood is termed brittle. 

 Pliability in wood from one species of tree or part of a tree 

 depends chieliy on specific weight; heavy wood is less 

 pliable than light wood. The branches are less pliable than 

 the stem, and the stem than the roots ; the liner rootlets are 

 used as withes. The rhizomorphs of the honey-fungus 

 (Armillarea incllca) are more pliable than the finest rootlets 

 of trees. Soft broadleaved wood is generally more pliable than 

 hardwoods, but on the other hand the wood of Hicoria alba is 

 much more pliable than the lighter, brittle wood of II. ainara. 



Rapidity of growth favours pliability, and coppice-shoots, 

 such as osier-willows and shoots of oak, birch, ash, elm and 

 hazel are very pliable. 



As lignin in woody tissues specially determines hardness 

 and strength, so cellulose confers on wood toughness and 

 pliability. The less the illumination under which the tree 

 has been grown, the more pliable it is. The very pliable 

 coppice-shoots are nourished chietly by reserve material from 

 the stools and roots and get very little nourishment from 

 light. The produce of thinnings is tough and pliable, but 

 not so hard and elastic as well-lignified steins grown under 

 complete illumination. [Woods grown on northern aspects 

 are more pliable than the harder and more lignified woods 

 grown on southern and western slopes, and the same is true 

 for woods grown on moist soil, as compared with dry calcareous 

 soil, or peat, which produce brittle wood. Tr.] 



Moisture increases the pliability of all woods. Hence in 

 freshly felled trees, the sapwood is tougher than the heart- 

 wood ; hardwoods when wet are tougher than when they are 

 dry, but the loosening of the walls of their tissues by Lho 

 water preponderates over the resulting toughness (<;/'. p. 87). 



Heat also increases pliability if precautions are taken to pre- 

 vent evaporation; heat and moisture acting together render wood 

 extremely pliable, so that steamed rods and planks can be bent 

 just as if they were formed of homogeneous material,'- as in 



* \V. Exiicr, ' Das IJii'^i;,, ( j,. s Hol/f.s." /i:ntr:ill)l:ilt, f. tl. jjes. Korst \\vsrn. 



is?*;. 



