344 ESSENTIALS OF BOTANY 
hard woods. There are no ducts, and the main bulk of 
the wood is composed of rather long closed tubes (¢racheids) 
which taper to a point at each end. The rings plainly seen 
on the cross-section of some kinds of coniferous timber are 
Fic. 282. Forest of Hard or Yellow Pine (Pinus palustris) on Southern 
Coastal Plain of the United States. 
(After Frye.) 
due to the difference in diameter of the tracheids formed 
in early spring and later on (Fig. 233). 
418. Hard Woods. — North America furnishes more spe- 
cies of trees valuable for hard-wood timber than any other 
region of similar area with a temperate climate. About 
eighty kinds are of economic importance, and of these 
six or eight are oaks, classed for commercial purposes as 
white and red or black oaks. White oak is stronger than 
