THE CORTEX, OR BARK. 291 



THE CORTEX, OR BARK. 



273. The Cork Oak, Quereiis Suber (family Cupuli- 

 fercB), is found in the southern part of Europe and the 

 northern part of Africa. It has oval, dentate, evergreen 

 leaves. The thick mass of cork which it develops is 

 removed periodically, and constitutes the cork of com- 

 merce. A corky layer, or periderm, begins to be developed 

 when the tree is two or three years old. The first cork 

 that is produced is very inferior, but after its removal good 

 cork is yielded. When the tree is five years old, the first 

 worthless layer can be removed without injury to the 

 phellogen, or cork-producing cambium. This is done by 

 making vertical and horizontal incisions, reaching almost 

 to the generating layer of cells or phellogen, within ; the 

 bark is then carefully pried ofi". This process cannot be 

 performed with safety during the period of rest of vege- 

 tation, nor during the active renewal of growth in the 

 spring; it can be done, however, between May and October 

 without in the least harming the phellogen, provided the 

 latter is not exposed to rain. The layers become two-thirds 

 to one inch (or more) thick, and are removed every eight 

 or ten years. When the trees are fifteen years old, a valu- 

 able layer may be removed. Cork continues to be pro- 

 duced till the trees are one hundred or one hundred and 

 fifty years old; that is best, however, which is removed 

 from trees between fifty to one hundred years old. The 

 cork that grows in warm regions is better than that pro- 

 duced in cold climates ; and that from trees on the mount- 

 ains is better than that from trees in swamps. It is said 

 that the thick branches and the south side of the trunk 

 yield better cork. When removed, the layers of cork are 



