DEFECTS AND UNSOUNDNESS. 71 



pine are repeatedly tappet! for resin from an early period in their 

 lives the lower part of their stems may become quite unfit for 

 timber, especially if decay ensues, as is usually the case. 



[The only European tree which can be economically tapped for 

 resin is the Cluster pine, provided the trees are not tapped till 

 sufficiently large to be used for railway-sleepers, small beams or 

 pit-timber ; the wood then becomes very hard and heavy from the 

 accumulation in it of resin, and if all the part which has been tapped 

 is removed after the tree is felled, being tit only for firewood, the 

 inner untapped portion of the wood may be utilized, as above. — Tr.] 



(i) Resin-galls. — The so-called resin-galls in the interior of 

 stems of old spruce and other conifers are also prejudicial to the 

 use of these stems as timber. H. Mayer states that these galls 

 are due to the fact that during the active life of the cambium, 

 resin is pressed into the cambium-zone from the horizontal 

 resin-ducts, these deposits of resin being afterwards occluded, 

 as in the case of wounds. Isolated trees are more subject to 

 resin-galls than those grown in a dense w^ood. 



2. Defects ill Tuiihar oicin;/ to Disease in the Woody Fibres. 

 (a) General Account. 



The resistance w^hich wood offers to decay will be described in 

 the section on the durability of timber. At present, the only 

 question is as to the extent to which standing trees which have 

 become decayed may be utilized. 



The ultimate materials into which decomposed wood is 

 reduced are carbon dioxide, ash, water and the intermediate 

 products termed humus. Decay in living trees may be dis- 

 tinguished by the colour, as wood suffering from red-rot or white- 

 rot ; the greenish colour of some rotten wood, chiefly beech and 

 oak-wood and due to a fungus (Peziza (enuiinosa), being of 

 rarer occurrence. Decaying felled wood suft'<;rs from dry-rot. 

 As already stated under Forest Protection, the mycelia of fungi 

 contain ferments, which act on the cell-walls ; some of these 

 ferments decompose the lignin only, leaving whitish cellulose, 

 and others the cellulose, leaving dark ligneous substances. 



Decay in standing trees may be eflfected either by means of 

 parasitic fungi, which obtain entrance into the wood through the 



