67 



In seasoning, the wood loses the water stored up in it ; as it evaporates 

 from the cell wall on the outside it is supplied from the cell-lumen on the 

 inside no shrinking of cell-walls takes place until the water of the lumen 

 is exhausted and then the cell-wall must give up its water, the molecules 

 composing the cell walls draw closer with the water molecules removed by 

 the dry air the cell or cell-tissues shrink. The thicker cell-walls of the 

 summer-wood contain of course the most water and hence shrink also more 

 than the spring-wood cells. Hence, the ring-porous woods, like the oak, 

 shrink more unevenly, and are liable to warping and checking. The pith 

 ray cells lying in different directions also shrink in different direction more, 

 and other source of season checks is due to them. 



While then the complicated structure of the ring-porous woods fur- 

 nishes greater strength structurally, it also imposes greater care in their 

 handling. 



In general, the heavier wood is also the stronger, and the quality of 

 the wood, with trees of pronounced summerwood zones, varies 

 from the centre of the tree to the periphery, according to the 

 rapidity of its growth. Since, as a rule, the rate of growth in diam- 

 eter is greatest between the 40th and 80th year, the heaviest and strongest 

 wood would lie in that part of the tree. And as the wood does not change 

 in structure it was also strongest when it was still on the outside of the 

 tree, i.e., when it was "sap-wood." In old age, to be sure, the tree growing! 

 slowly makes poorer wood and hence in old trees the sap-wood, not because 

 it is sap-wood, but because it is old wood, is weaker. 



