638 UTILIZATION OF BARK AND ITS CONSTITUENTS. 



oak (J. nibra, contains only 4 per cent, of tannin, but in the 

 west of America, Q. densiftora, and in Japan, Q. dantata, are 

 the chief oaks that yield tannin. 



(b) Climate. Undoubtedly the chief factor in the produc- 

 tion of tannin is the climate. All tanning materials are the 

 richer in tannic acid, the hotter the country in which they 

 are produced; this is the case with galls and other substances, 

 and is equally true for oak-bark. All factors, therefore, which 

 heighten the temperature for the tree, southerly aspect, loose soil, 

 open crop, increase the amount of tannin in the bark of oak-trees. 



The mild climate of the Khine-Valley and the adjoining 

 districts, especially the Moselle-Valley, Eheingau, the district 

 of the Saar and the Odenwald, affords the best oak-bark 

 coppices in Germany. Oak-bark is also produced commer- 

 cially in the Silesian hills, Saxony, the North German plain, 

 Brunswick, Mecklenburg, etc., but it cannot compete with 

 Ehenish bark. Many districts in Austria, Hungary and 

 France are situated more favourably for successful production 

 of bark, which is there produced in fairly large quantities. 

 Districts where the vine is cultivated in the open, or where 

 at any rate the better classes of fruit trees flourish, may be 

 cited as suitable for a remunerative yield of oak-bark.* 



(c) Soil. The more suitable the soil is for the growth of 

 oak, especially when the climate is suitable, the more quickly 

 the oak grows, the more and better tannin does its bark yield. 

 It is true that coarse bark comes earlier under such circum- 

 stances, so that the rotation must be shorter, the better the 

 soil ; on a good soil the crop may be denser, as a dense 

 crop retards the formation of rhitidome. A wet soil is pre- 

 judicial to oak-bark coppice. The mineral nature of the soil, 

 at least in good climatic localities, appears to be unimportant, 

 and provided the soil is deep, porous and moist, it is indifferent 

 whether the subjacent rock is sandstone, granite, schist, 

 porphyry, limestone or diluvium. 



(d) Age. Besides the parenchyma of the cortex, it is espe- 

 cially the longitudinal parenchyma of the bast, in which chiefly 



* From the above, it is eviden* that oak-hark coppice prove* moiv remunera- 

 tive in the south of England, Wales and in heland, than in Scotland. Unfor- 

 tunately the, price is now so low that the production of oak coppice is being 

 abandoned in Mritain. 



