148 PROPERTIES OF WOOD. 



becomes occluded, but only after incipient decay of its 

 surface ; this decay proceeds slowly round the wound in all 

 directions, so that when the tree is ripe for felling, from 5 to 

 20 per cent, of the cross-section at its base and about 10 feet 

 of its length are affected. This unsound heartwood is liable to 

 further decay and cannot be impregnated by antiseptics. 



It is usually difficult to diagnose the health of a standing tree. 

 The presence on its stem of bracket-like sporophores of Polypori 

 and other fungi is a certain proof of unsoundness ; all other 

 symptoms are deceptive, such as : projecting occluded lumps in 

 the stem ; swellings in the stem especially near its base (Fig. 

 55) ; partly occluded snags with central depressions ; presence 

 of ants or mice among the roots. There is no difficulty in ascer- 

 taining whether or not a felled tree is sound; the axe can be used 

 to cut into projections on the stem, while an inspection of the 

 sawn surface of its base is usually sufficient ; specially valuable 

 boles may be split in two, as is done in the Spessart. 



I. Abnormal Scents. 



Any abnormal scent in wood, that may, however, be detected 

 for only a few species, e.g., oakwood, denotes decay. When 

 decay has gone very far the wood has a mouldy scent like that 

 of fungi. 



c. Diminished Hardness and Sp. Weight. 



If stem-wood is considered normal as regards sp. weight 

 and hardness, branch-wood, especially the horny heavy 

 branches of conifers is abnormally hard and heavy ; root-wood 

 is abnormally light ; narrow-zoned coniferous wood is heavy, 

 and narrow-zoned broadleaved wood, especially of oak, is 

 light. 



d. Defects in the Economic Properties of Wood. 



In order to avoid repetition, it is sufficient here to refer to 

 defective shape only. Besides a bent or conical shape in 

 stems, that have been discussed already, excentric growth 

 deserves mention. The woody layers are excentric when the 

 pith on a cross-section is not the centre of the more or less 

 circular annual zones of wood around it. All plant-part 



