664 UTILIZATION OF BARK AND ITS CONSTITUENTS. 



surrounds the whole stem and is not replaced by rhitidome, 

 as in the cork-oaks of the westerly Mediterranean countries 

 (south France, south Spain, Portugal, north Africa (including 

 Tunis), Corsica, Italy, Sicily and Greece), a material is pro- 

 duced, which in its special qualities, elasticity, lightness, 

 softness, durability, impenetrability by gases and spirituous 

 liquids, can be replaced by nothing else. 



Cork (suberin) is distinguished from wood by its higher 

 contents of carbon and hydrogen ; its chemical composition is : 



C ... 66 per cent. 



H ... 8-5 



... 22-8 

 N 1-9 



The thin-walled cells of cork do not consist entirely of 

 suberin, but this substance is stored in large quantities in the 

 fine skeleton of lignin and cellulose of their walls. Every wall 

 common to two cells contains a lignified medial lamella, on 

 both sides of which is a purely suberous layer, and on this, 

 forming the innermost coating of the cell, is a thin lamella of 

 cellulose. The layer of cork is the thickest of the three 

 lamellae ; only in thick-walled cork-cells (resembling late-wood 

 and formed as late-cork in autumn), does lignin preponderate. 



The two oaks (Qucrcus Suber and Q. occidentalis) , in the 

 countries already referred to, are subject to a regular system 

 of management : the first layer of cork (male cork) is full of 

 cracks, unevenness, impurities and stone-cells, and is therefore 

 of little use. When the trees are about 20 years old this cork 

 is removed by means of a sharp trimming-axe, so that the 

 phellogen below is uninjured. Then the phellogen produces 

 annually fresh fine layers of cork with visible annual rings. 

 This useful, female cork is cut off in layers surrounding the 

 stem and a meter long, every 8 to 10 years. In a young tree 

 only the lowest section is removed, next time another higher 

 section as well, and so on, till the boughs are reached and are 

 also stripped of cork. In order not to endanger the life of a 

 tree, eventually only one section is stripped in a year. The 

 strips of cork are pressed flat and sold. Corks are cut from 

 these strips, parallel to their length. Thin strips of cork are 



