632 UTILIZATION OF BARK AND ITS CONSTITUENTS. 



sticks, or for light fancy furniture. In particular a red colour 

 is prized, that affects the outer rind of a bamboo after 

 exposure to smoke in a chimney, or it has been kept in huts 

 without chimneys. 



As soon as rhitidorue or dead bark is formed, and bark- 

 scales appear on the exterior of some of our trees such as 

 larch or pine, the tannin in them becomes oxidised and turns 

 red or brown, resembling the transformation of living sap wood 

 into drier heartwood, that is dead in conifers. In trees such 

 as beech, hornbeam, silver-fir, etc., where rhitidome is not 

 formed, or is formed only when the trees become old, the bark 

 is usually grey, owing to its incrustation by lichens ; in birches 

 the white betulin gleams through the cell-walls. 



When the bark-scales become red the durability of the bark 

 is increased considerably, just as is the coloured heartwood ; 

 if the cortex is wounded the tissues exposed to the air redden 

 rapidly, a process of oxidation that protects the wound, the 

 protection afforded being increased by the subsequent provision 

 of a layer of cork. This explains the great durability of very 

 thick barks ; as, however, the thick barks of oaks, larch, old 

 pines and Douglas-firs, are separated with greater difficulty in 

 large, regular pieces from the sterns, than from those with 

 thin and small scales-; it is the latter, e.g., spruce and birch, 

 which are peeled during the life of the trees, and used for 

 covering roofs that are exposed to the rainy west wind. The 

 birch produces a scaly or stony bark only late in life, and 

 owes the great durability of its bark to the betulin in its cells. 



The heating-power of the bark is less than that of the wood, 

 even in conifers, in which, according to Mayr's investigations, 

 there is more resin than in the wood ; the coarser the bark, 

 the better it is as a combustible. It is peeled off fallen trees 

 in summer in large flakes, about one meter long, or is hacked 

 or beaten off them in winter, and used as combustible bark. 

 This bark is piled in stacks and sold, or given unmeasured to 

 poor people, or to the wood-cutters. Owing to its greater 

 heating-power, birch-bark is used as kindling material, as is 

 ver} 7 resinous pine wood. 



Thick pieces of willow bark (Salix alba), which is very 

 light, serve as mrunmars for iishing-nets ; fresh spruce bark 



