The Oaks : General Division. 211 



size to ■which the more important species grow, the vast age that 

 they attain, and the hardness and durability of the timber. Since 

 the introduction of iron as a building material, the oak has lost 

 much of its importance in ship-building and for structures requiring 

 great solidity and strength, such as bridges and large buildings for 

 business purposes or public use in cities ; but the better kinds of 

 oak will always be valued among the most desirable for forest 

 planting, and under favorable conditions as the most profitable that 

 can be grown. 



847. The oaks are chiefly natives of the north temperate zone, 

 but some occur upon mountains within the tropics, in the Malay 

 archipelago, and in South America. None are found in Australia ; 

 one genus only of the family is found in the south temperate zone, 

 and a few are found within the Arctic- circle. 



848. About 250 species of the QwercMs, or oak genus, are known 

 to botanists. They are arranged by De Candole ' into six sections, 

 four of which are found only in South-eastern Asia. About forty 

 species occur native within the United States. They may be con- 

 veniently arranged into two classes, viz., the "white" and the 

 '-' black " oaks. 



849. The white oaks, are so called from the grayish or ash-colored 

 tint of the bark, which often tends to separate into scales. The 

 wood is tough, dense, and excellent for cooperage, wagon-making, 

 and other uses requiring closeness of grain, strength, and durability. 

 The trees are slower in growth than the other divisions to be men- 

 tioned, but owing to the superior quality of the timber, they may 

 prove more profitable for planting, although longer in coming to full 

 maturity. They are excellent for fuel and charcoal, and most of 

 them are desirable for ornamental planting. 



850. The black oaks, have a bark which is dark, rough, and deeply 

 cracked. The wood is brittle, porous, and a poor fuel. It is so 

 porous that it can not be used for casks for holding liquids. The 

 peduncles or fruit stems are short or wanting, and the acorns gener- 

 ally ripen the second year, but to this there are some exceptions. 

 Their growth, as compared with the white oaks, is very rapid, gen- 

 erally as two to one, and even more. There is generally less dis-. 

 tinction between the heart-wood and the sap-wood, and they occur 



^Prodromus, Vol. XVI. 



