BICOTYLEDONES. 189 



Nut-Galls of commerce, are morbid growths on the leaves 

 of Q. Lusitanica, var. infedoi-ia, caused by the punctures 

 made by an insect (genus Cynips). The tree grows in 

 the Mediterranean region, and the galls are valuable for 

 the tannin they contain. The White Oak (§. alba) of 

 the United States is of great importance for its timber. 

 The Live Oak of the Southeastern United States, having 

 small evergreen leaves, has heavy, strong, and durable 

 wood, used in ship-building. The Cork Oak (§. suber) 

 grows in Southern Europe and Northern Africa; the 

 corky layers of the bark increase much in thickness, and 

 are carefully removed every eight or ten years, and furnish 

 the cork of commerce. The Black Oaks, as Black-jack 

 ( Q. nigra). Red Oak ( Q. rubra). Scarlet Oak ( Q. eocdnea), 

 etc., produce a less durable and coarser grained wood than 

 the preceding (White Oaks). From the bark of the 

 Scarlet and Quercitron ( Q. coceinea, var. iinctoria) Oak, a 

 yellow dye. Quercitron, is obtained. The California Tan- 

 bark Oak (§. densiflora) is a beautiful tree one hundred 

 feet high, and bears fruit in curious chestnut-like, spiny 

 cups. 



4. Juglandaceae. The ^A^alnut family comprises 

 trees and shrubs, with pinnate leaves, and a hard one- 

 seeded nut. This small family (about thirty species) has 

 representatives in North America and Asia. The light 

 brown wood of the Walnut of the Old World {Juglans 

 regid) is highly prized in the manufacture of furniture, 

 piano-cases, gun-stocks, etc. The thin-shelled nuts are 

 imported to this country under the name of English 

 Walnuts. The Black Walnut {J. nigra), a giant tree of 

 the United States, furnishes a dark-brown timber, as valu- 

 able as the preceding; and like it, extensively used in 



