I'TSSIl'.IIJTY. S7 



fibres; it is indifferent whether this he radial or tangential. 

 Penetration by an instrument is then possible only it' the 

 fibres are severed, while their severance is rendered more 

 difticult owing to their compression by the instrument. 



Fineness of grain is the next important item favouring 

 iissibility, a straight uninterrupted course of the fibres 

 renders a wood fissile; everything that favours or diminishes 

 fineness of grain in woods increases or lessens their iissibility. 

 Twisted fibre occurs sometimes in entire stems, and normally 

 in the rootstock or at the junction of ihe stem \\ith a branch ; 

 this diminishes the lissibility of the wood. Kissibilit 

 annulled absolutely when the fibres alter in direction in 

 consecutive annual rings, as in ( Juiacum-wood. 



High medullary rays, or numerous fine rays inert 

 Iissibility in the radial direction. 



Moisture softens the cell-walls, so that contiguous cells are 

 separated more easily, but they also became lougher. In 

 hardwoods, the increased divisibility out-balances the tough- 

 ihat they are split more easily when wet than when 

 they are dry. In the Spessart freshly-felled oaks are split 

 longitudinally to test their soundness. The opposite is the 

 case with softwoods: their toughness when wet out-balances 

 their divisibility ; therefore they arc more fissile when dry. 



With woods that are equally moist, a higher temperature 

 increases fissibility unless it also dries the wood. If the tem- 

 perature is below freezing-point and the wet wood free/cs, its 

 fissibility is at once prejudiced ; frozen wood breaks with 

 a conchoidal fracture like a block of ice, as it resembles 

 ice closely in its physical properties. This is another clear 

 proof that when wood freezes, water is not exuded from the 

 cell-wall, otherwise the sapwood of softwoods, (specially of 

 conifers, would become more; fissile than before it was fro/en. 

 As water \\hen fro/en in the cell-walls reduces the fissibility of 



wood, the same result will follow when other substances replace 

 water in the cell-wall. 



All colouring-matters and resin therefore reduce fissibility. 

 In extreme cases, when the resin hardens into rosin with which 

 the wood becomes impregnated, lissibility disappears; such 

 wood resembles frozen wood in this respect. 



