I.] CORYLACE.E. 213 



of the Valonia'Oak (Q. sEgilops) are also very"astringent, 

 and are imported in large quantities for the use of tanners 

 and dyers. In 1871, 27,706 tons were imported. From 

 the gallic acid contained in the wood, the timber of the 

 Oak is apt to become black when immersed in water 

 containing salts of iron, which, combining with the gallic 

 acid, form a natural ink. Hence the frequent blackness 

 of bog Oak, and the black stains around iron nails and 

 bolts driven into Oak timber. 



Tannin and gallic acid, used in ink- making and for 

 photographic purposes, are chiefly obtained from the 

 galls produced upon the leaves and twigs of Q. infectoria, 

 in Asia Minor. Similar (smaller) galls, called "oak- 

 apples," are very common upon the leaves of common 

 Oak. The galls are excrescences, caused by the punc- 

 ture of different species of Cynips, small flies which lay 

 their eggs beneath the epidermis, and, in some way not 

 well understood, induce the abnormal, development of 

 tissue forming the gall. 



Decaying branches of Oak are occasionally stained a 

 verdigris green by a fungus (Peziza cemginosd). This 

 stained wood is used for fancy work at Tunbridge Wells. 



Two species (or rather varieties of one species) of Oak, 

 differing in the length of time required to mature their 

 acorns, afford cork, so largely used in making bottle- 

 corks and bungs. The species are Q. S^lber, ripening its 

 acorns in the first season, and growing in the South of 

 France, Spain, and Algeria, and Q. occidentals, a native 

 of the Atlantic side of France and Portugal. Cork is 

 the outer bark, removed from the tree at intervals of from 

 six to ten years after it has attained about thirty years of 

 age. Cork previously collected is of inferior quality. 

 The bark is heated, flattened underweights, and allowed 

 to dry slowly. It is said that the operation of removing 

 the cork favours the healthy growth of the tree. 



Division. Achlamydeas. 



59. Natural Order Betulaceas. The Birch Family. 



DISTRIBUTION. Almost wholly confined to the cooler 

 parts of the north temperate zone in both the Old and 

 New World. British genera 2, species 3. 



