84 TECHNICAL PROrp:UTIE.S OF WOOD. 



timber. Even experienced timber-merchants may find it difficult 

 to decide iu certain cases whether a piece of timber is sound 

 or not, but there are certain marks of sound timber which have 

 been ah-eady referred to (p. 77). 



There is always a danger when a tree is very old that the 

 resulting timber will not prove sound, and experience shows 

 that middle-aged timber gives better results than very old 

 material. Evidently the danger from fungi, or from rot arising 

 from broken branches, continually[iucrcases with the increasing 

 age of a tree. Exceptions may be made here as regards Scotch 

 pine and larch, on account of the increasing proportion of heart- 

 wood and accumulation of resin with increasing age, but this is 

 under the proviso that the tree is still young enougli to continue 

 increasing in girth. 



3. Treatment of the Wood after FelUncj. 



The treatment of the wood after felling is of greater import- 

 ance for its durability than the season of felling. The nature 

 of the exposure of the wood during its shorter or longer stay in 

 the forest, the methods of transport, and the subsequent mode 

 of storing it until it is converted and utilized, are the chief 

 factors which determine its durability. 



In every case, the greatest efforts should be made to avoid 

 everything which might favour infection by fungi and their con- 

 sequent development ; this can be attained only by measures 

 securing a steady drying process from the moment the wood 

 has been felled until it is utilized. If the wood has become 

 infected by fungoidal spores whilst still in the forest, as in the 

 case of summer-felled wood, and it is prevented from drying 

 sufficiently, whilst lying in the forest, during transport and 

 especially when in depot, dry-rot must ensue to a greater or 

 less degree, the extent depending on the interval between the 

 felling and the utilization of the wood. 



The powers of resistance of diftVrent species against this 

 threatened danger vary considerably ; soft broad-leaved species 

 are most exposed to it, then beech, spruce and silver-fir. 



Since spruce and silver-fir woods of the higher mountain 



