272 THE UTILISATION OF WOODLAND PRODUCE. 



logs, and splitting and warping are likely to occur if logs are 

 sawn into planks before seasoning. 



3. As REGARDS RELATION TO WATER, upon which shrinking, 

 cracking, splitting, warping, and expansion depend, wood 

 shrinks more or less in seasoning, and thus tends to warp, 

 the dense, slow -drying heartwood shrinking more unequally 

 than sapwood, and resinous Conifer wood more gradually than 

 that of broad-leaved trees. But the specific weight of wood 

 gives no indication of its liability to shrink or warp. Conifer 

 wood that is very resinous, and wood that has been steamed, 

 are least liable to warp. Lime, Beech, Hornbeam, Elm, Chest- 

 nut, Birch, and Alder shrink most, and pedunculate Oak and 

 Conifers least. Shrinkage is least longitudinally (being only 

 nominal), greater radially (about 6 per cent), and greatest 

 tangentially (about 10 per cent) ; and it is this want of uni- 

 formity in the rate of shrinkage in different directions that 

 occasions warping, cracking, and splitting. The more rapid the 

 shrinkage, the greater the tendency to warp, crack, and split; 

 hence summer-felled timber is more likely than winter-felled to 

 do so, and barked logs crack and split more than those left with 

 bark on (which in Conifers would lead to bark-beetles breeding 

 in large numbers). Practically, in proportion as wood shrinks 

 in seasoning, it swells or expands again by absorbing water in a 

 damp state of the air ; and this must be allowed for in construc- 

 tion with timber. 



4. DEFECTS IN TIMBER are due to abnormal anatomic structure 

 and other conditions, and include branch-knots, twisted fibre, 

 wound-surfaces, and rind-galls completely covered, and shakes of 

 various kinds (simple or star-shaped heart-shakes, frost cracks, 

 cup- or ring-shakes), which all weaken its strength, and therefore 

 depreciate the value of timber for technical purposes. Frost- 

 ribs being mostly full of water, are called " water-shakes " by 

 timber -merchants. Branch-knots are commonest in shade- 

 enduring trees, which do not readily lose their side-branches. 



