FISSIBILITY. 39 



Soft: Spruce, silver-fir, horse-chestnut, black alder, white 

 alder, birch, hazel, juniper, larch, black piue, Scotch pine, bird- 

 cheny, sallow. 



Very soft : Paulownia, Weymouth-piue, poplars, aspen, most 

 willows., lime. 



Section YI. — Fisslbility. 



By the fissibility of wood is meant the property it possesses of 

 being split by a wedge driven into it in the direction of the 

 fibres. 



Fissibility is clearly a form of hardness ; wood is not merely 

 affected by the actual contact of a wedge, for the fibres separate 

 from one another in front of the wedge, and the ease with which 

 this happens is a measure of the fissibility of the wood. Resistance 

 to fission is the opposition wood offers to the passage througli it 

 of a wedge. Fissibility is chiefly afi:ected by the structure of the 

 wood in question, and also, to a certain extent, by the elasticity 

 of its fibres; other factors which must not be overlooked 

 intervene in varying degrees. 



1. Structure (if tlie Wood. 



Straight and long fibres render a wood fissile, and this is the 

 case with most conifers and all rapidly-growing woods. Free- 

 dom of a stem from branches and knots is another important 

 condition for fissibility, and this should be the case from the 

 earliest years of the tree's life. 



A wavy or twisted, unhomogeneous condition of the fibres, 

 owing to knots, wounds, bent fibres, or dormant buds, implies 

 considerable power of resisting fission. Thus, it is difficult to 

 split the wood of elms, birch, planes and most maples ; also of 

 slowly-grown trees of other species, or those which have grown 

 in a roomy condition, from wide planting, such as branchy 

 spruce. Branch and rootwood, owing to twisted, knotty 

 structure, is harder to split than stemwood, and no part of a tree 

 is harder to split than the stump, where the tap- and side-roots 

 unite to form the bole. Trees with twisted fibre are specially 

 hard to split, and it is found that those twisting from left to 

 right (against the sun's apparent course) are harder to split than 

 those twisting in the opposite direction. 



