DEFECTS IN TIMBER. 273 



Knots in Conifers become saturated with resin, and then 

 (especially in Larch) are very hard to plane, though they 

 enhance the ornamental appearance of the wood. Twisted fibre 

 is commonest in Chestnut, Oak, Elm, Beech, Sycamore, and 

 Scots Pine, and makes wood more liable to warp. 



5. UNSOUNDNESS is due to fungus disease. The chief kinds 

 of unsoundness are canker, red-rot, white-rot, white-piping (Oak), 

 and blueing of Conifers (especially Scots Pine) ; but root-rot, 

 branch-rot, and stem-rot are common in old trees growing on 

 unsuitable or imperfectly drained land. And even after it is 

 converted and used in construction, timber, especially if only 

 partially seasoned or in a damp place, is liable to be attacked 

 by dry-rot (due to Merulius lacrymans) and other saprophytic 

 fungi. 



The chief fungi causing unsoundness are as follows (see also Part III., 

 chap, iii.) : 



Canker : Peziza (Larch) ; Nectria (Ash and Beech mostly) ; JEcidium 

 elatinum (Silver Fir) ; Cronartium (Peridermium Pini : Scots Pine). 



Red-rot, from decomposition of cellulose : Tramctcs Pini (Scots Pine), 

 Pomes annosus (Pine, Spruce, Silver Fir) ; Polyporus sulphureus (Oak and 

 Birch chiefly) ; P. betulinus (Birch). 



White-rot, from decomposition of lignin : Agaricus melleus (all kinds of 

 trees); Fames igniarius (Oak and Willows mostly); F. fomentarius (Beech, 

 Oak, Elm) ; Polyporus dryadeus (Oak) ; Hydnum diversidens (Oak, Beech). 



White -piping is caused by Stereum hirsutum (Oak). 



Blueing of Conifer timber : Ceratostoma piliferum. 



V. The Mechanical Properties of Timber are of the first 

 importance, as they govern its relation to external influences. 

 They include strength, elasticity, flexibility, toughness, fissibility, 

 hardness, and durability. 



1. STRENGTH in timber is the resistance offered to any force 

 tending to separate its fibres, whether applied longitudinally as 

 if pulling the fibres apart (tension), or pressing them together 

 (crushing), or at right angles to the grain (transverse-pressure 

 or breaking-strain), or so as to twist the fibres (torsion), or more 



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