18 



OF WOOD IN GENERAL 



a minimum of one two-hundredth of an inch (0-2 mm.).-^ Many 

 local causes, especially exposure to wind, produce excentricity 

 of growth, few trees presenting a truly circular cross-section or 

 a truly central pith, though this is more common among pines 

 than among other trees. Branches almost always present an 

 excentrically oval section, the pith nearer to the upper surface. 

 The summer-wood in each ring being darker, heavier, and denser. 



Fig 12 —1 Piece of wood of Spruce (JPicea eocUsa) ■with the baik lemoved, natural 

 si7e 2 A portion from the neaiest upper outside angle of 1, showing wood neai the 

 outside of an annual rmg, magnified 100 times (Prom Hartig s Ttmbeis and koto to 

 Inow than, by permission of Dr Somerville and Mr David Douglas ) 



its relative proportion to the spring-wood largely determines the 

 weight and strength of the wood, so that colour becomes a valu- 



i Poplars grown m moist groimd may reach a diameter of 14 mehes in 8 years. 

 Laslett lecords {Timber and Ttmher-trees, ed. 2, pp, 44-5) exceptionally fine English 

 Oak and Elm, and an aveiage drawn from seveial specimens of Canadian Oak and 

 Elm which gave the followmg number of imgs at 6, 12, 18, and 24 inches diameter : 



English Oak, - 

 Canadian Oak, 

 English Elm, - 

 Canadian Elm, 



5111 



12 m 



18 m. 



24 in 



13 



19 



24 



30 



49 



105 



160 



216 



10 



16 



25 



36 



80 



156 



252 







