FORESTRY. 95 



eight or ten years, the later crops yielding- a better product than the 

 earlier ones. The expense of each harvest from a single tree is about 

 2 cents. 



Individual trees differ greatly in the rate at which cork is formed. 

 As a rule, the best product is that which develops most slowly. Rap- 

 idl}^ growing cork is more abundantly veined with loose tissue, which 

 diminishes its value. The cork is sometimes seriously injured on the 

 tree by the ravages of ants, which build galleries in it. The tree has 

 also other insect enemies. 



The cork, when cut, rolls up into tubes of the size of the trunk from 

 which it was taken. It is first pressed out into sheets, then l)oiled, 

 and finally the crust of bark is removed by scraping. Boiling increases 

 the bulk by about one-tifth and renders the cork more elastic. 



An acre of cork oak in full production jaelds a net annual revenue of 

 about $2. The product from a single tree is worth from 4 to 10 cents 

 a year after all expenses are deducted. Algerian cork sells at from 3i 

 to 10 cents per pound, 



TAN BARK. 



The forests of Algeria furnish a large amount of bark for tanning. 

 The annual export of tan bark, chiefly to Great Britain and Itah', 

 amounts to about $200,000. A considerable quantity is also consunied 

 in the colony itself, the manufacture of leather being an important 

 industry among the natives. 



Most of this bark is furnished by several species of oak. The Ker- 

 mes oak {Qnercus coccifera) ranks first in production, the bark of the 

 root being used. The forests of cork oak, especially those belonging to 

 natives, also furnish a large quantity. The collection of the bark is 

 generally done in such a way as to kill the tree, although if proper 

 precautions were observed the forests could be exploited for tan bark 

 without diminishing their production of cork. The bark of this oak 

 yields about 19 per cent of tannin, A single tree will furnish several 

 hundred pounds of bark, a ton of which sells for from $22.50 to 137.50. 



Various tannin-producing plants, such as Australian species of acacia, 

 which furnish the wattle bark of commerce, canaigre, and the Valonia 

 oak, have been recommended for cultivation in Algeria, but none of 

 these has yet become of practical importance. In Tunis experiments 

 are being made by the government in the cultivation of the Sicilian 

 sumac {Rhus co7'ia?'ia), the powdered leaves of which are a valuable 

 material for tanning. 



ALFA. 



The Arabs use the word "half a" in much the same way as the term 

 "bunch grass" is used in the western United States to designate any 

 coarse, rush-like grass that grows in tufts. The "alfa" of the French 



