1-0 TKCHXICAL PROPERTIES OF WOOD. 



The structure of the mcdunary rays has very great influence 

 on the fissibility of a wood, for they are iu the phiue in which 

 the principal splitting action lies, so that oaks and beech, which 

 have large rays, are easily split. Conifers possess extremely 

 small but very numerous medullary rays, which are also very 

 fine, consisting usually of only one row of cells ; this is also the 

 case with poplars, willows, alders, birch, limes, hazel, kc. 

 Thus, in such cases, the longitudinal fibres lie straighter 

 between these numerous fine rays than they do between larger 

 ones, and the wood is easily split. 



The coherence of woody fibres in this case means chiefl-y that 

 of the longitudinal fibres lo the medullary rays, which in some 

 species appears to be considerable, as, for instance, iu the cork- 

 oak, elms, hornbeam, sycamore and other maples. In most 

 woods, however, this coherence is slight. The coherence between 

 the annual woody zones is greater, and this is probably due to 

 the fact that most medullary rays run uniformly through a 

 number of annual zones of wood binding them together and 

 thus increasing their mutual colu'rence. It is, therefore, easier 

 to split wood radially than tangentially. Fission along annual 

 zones is easiest in conifers, poplars and aspen. 



2. Elastuiti/ and Flixihiliti/ of Fibre . 



Elasticity always increases fissibility, for the more elastic a 

 wood, the faster the splitting precedes the wedge, and the 

 wider the cleft opened in the wood. Elasticity of fibres varies 

 with their length and straightness, advantages peculiar amongst 

 others to conifers. In the absence of elasticity, either brittleness 

 occurs, as in short-fibred woods, or flexibility, as in the case of 

 many soft broad-leaved species ; in the former case, a splitting 

 action breaks the fibres ; in the latter, they yield before the 

 wedge without transmitting the shock any further. 



8. Moisture, (Cc. 



Wood splits best when either green or quite dry ; half-dried 

 wood is least fissile. This is due, when the wood is green, to 

 the flexibility of the fibres, and when it is quite dry, to their 

 elasticity. 



