USES OF CORK 341 



very uneven because the bark scales off in chunks. 

 This is because the courses of the phellogens are irregu- 

 lar and curved, intersecting one another. The actual 

 nature of the cork formed also varies in different trees, 

 sometimes being hard and woody, while in other cases 

 the corky substances of the cell walls is very pure, 

 giving an elastic character to the bark. 



Uses of Cork. The " cork " of ordinary life is obtained 

 from the bark of the cork oak (Quercus suber) , an ever- 

 green oak native in the Mediterranean region. The first- 

 formed bark is rough, but after this has been removed the 

 bark subsequently formed is very uniform in structure, 

 and the corky substance of the cell walls very pure. 

 This bark is removed in sheets at intervals of several 

 years, boiled in vats to soften it, pressed flat, and then 

 cut up as required. The dark streaks seen in cork are 

 the lenticles, composed of loose powdery cells, which 

 are continuously formed by the phellogen, so that they 

 penetrate the whole thickness of the bark. Bottle 

 corks are always cut at right angles to the course of 

 the lenticels, i.e. parallel to the surface of the bark, 

 so that solid cork intervenes between the lenticels in 

 the length of the cork. If they were cut the other way 

 so that the lenticels ran through them from end to end, 

 the cork would not be gas and water tight. Bungs, 

 on the other hand, which are not intended to be gas- 

 tight, are stamped straight out of the cork sheet, 

 so that the lenticels run from top to bottom of the 

 bung. 



Cork tissue is not only gas and water tight, it is 

 also a very slow conductor of heat. Thus a jacket of 

 cork prevents the living tissues in the interior of a 

 tree-trunk from being heated or cooled too quickly 

 with external changes of temperature. This character, 



