ioo FORESTRY 



to transverse strain is as follows : Oak, Ash, Spruce, and 

 Scots Pine ; and in relation to pressure or crushing : Oak, 

 Beech, Acacia, Larch, Scots Pine, Spruce. 



Hardness affects the working of timber chiefly in two 

 ways, in its cleavage (separation of the wood-fibres longi- 

 tudinally), and in the resistance of wood to the penetration of 

 the saw in the transverse direction. The straighter and 

 longer the fibres of the wood and the larger and more 

 numerous the medullary rays, the easier does a timber split 

 or cleave. The timber of conifers is sawn through with less 

 difficulty than that of broad-leaved species, and timber which 

 is fresh and green gives less resistance in this way than that 

 which is dry or frozen. 



Elasticity. If wood when bent into a change of form 

 by the external application of force offers resistance, and 

 on being released, tends to resume its original shape, it 

 is said to have elasticity ; for example, Ash, Oak, and 

 Elm have this quality in a marked degree. Flexible wood 

 is different from this ; it retains its new shape after the 

 pressure is removed, but will not break as brittle timber 

 does. Birch, Aspen, Poplar, Spruce, and Hickory are 

 flexible woods. 



Durability. The durability of timber depends greatly 

 upon the treatment it receives and the use to which it is 

 put. Decomposition is most active when, by frequent changes 

 from a wet state to a dry one, unprotected wood allows the 

 entrance of fungi and insects. Wood well dried and 

 thoroughly seasoned, or that which is completely submerged 

 in water, remains sound exceptionally long. Faulty venti- 

 lation, especially of imperfectly seasoned wood, or where 

 wood comes in contact with the soil, leads to rapid decay. 

 The lasting qualities of timber are much affected by the soil 

 and situation where the trees are grown ; careful choice of 

 species should therefore be made at the time of forming 

 plantations. All that tends to the production of clean, 

 healthy trees favours the durability of the timber. 



The preservation of timber can be brought about by treat- 



