160 



FOREST UTILIZATION WOOD USES AND ECONOMICS 



to resemble wood have proved to be expensive and unattractive in 

 appearance. 



Every forester should have an accurate knowledge of wood struc- 

 ture and should know how to identify the many different species that 

 appear in our American markets.* 



Wood structure refers to the relative size, shape, appearance, and 

 form of the wood elements. These characteristics vary with each 

 species. This explains why some species are heavier, stronger, tougher, 

 and stiff er than others, why some are cross or straight grained, hard or 



B. 



C. 



FIG. 90. Photographs of wood as viewed under the microscope. A. Across the 

 grain. B. Along the grain tangent to the annual rings. C. Along the grain at 

 right angle to the annual rings. Resin canal is shown as the large opening in A. 

 This view also shows 3 l /2 annual rings. A is sugar pine and B and C are northern 

 white pine. These two species and western white pine compose the white pine 

 group. Photos by H. P. Brown. 



soft, and why some have a tendency to check and split whereas others 

 season rapidly and without injury. For example, the structure of oak 

 with its wide wood rays is responsible for its pleasing effect when it is 

 quarter sawed and polished to display the grain. The sapwood differs 

 considerably from the heartwood in structure and appearance. Some 

 species have a very thin sapwood, such as redwood, catalpa, red cedar, 



* For further treatment of this subject, see "Identification of the Commercial 

 Timbers of the United States," by H. P. Brown and A. J. Panshin, McGraw-Hill 

 Book Co., New York, 1934, and "Identification of the Timbers of Temperate 

 North America" by S. J. Record, John Wiley & Sons, New York, 1934. 



