LECTURE VIII. 



THE CHARACTERISTICS OF WOOD. 



The forester's business is not so much to produce trees, or even for- 

 ests, but the chief material which they furnish, wood ; and not only wood 

 merely, but wood of certain quality, fit for use in the arts. He must, there- 

 fore, not only be able to recognize the different woods and know their qual- 

 ities and their applicability for various uses, but more ! he must know how 

 differences in quality are produced and apply that knowledge in the produc- 

 tion of his crop. All the technical qualities weight, hardness, strength, ap- 

 pearance, and even color to some extent, and the behavior of wood can be 

 more or less directly traced to their variable structure the varying com- 

 bination of the cells, with thinner and thicker walls, larger and smaller 

 lumina (openings), and cell systems, which make the wood. 



Without going into details and microscopical distinction, a mere mi- 

 croscopic inspection with the magnifying glass of the gross features re- 

 veals much of the characteristics of the wood. A cross section 

 (across the bole) serves the purpose best although tangential sections 

 (parallel to the central axis) and radical sections (in direction of radius of 

 the cross secton) reveal also special features. 



Comparing cross sections of our northern trees of various kind, we 

 find that they can be classified in three classes differing clearly in appear- 

 ance of structure. The distinction is found by examining each annual ring 

 in itself, and the change from one ring to the other. 



This examination reveals that in each case there are two zones defined 

 in the ring of the year's growth, in most cases recognizable by color dis- 

 tinctions, namely the lighter colored interior part the spring-wood, so- 

 called because it is the first wood formed in spring and the summer-wood, 

 the last wood formed in the season. The former is lighter colored, because 

 formed of thin-walled cells with wide lumina, forming a loose, open struc- 

 ture, while the latter is dark colored, because of thick-walled cells with 

 small lumina, which reflect the light differently, forming a dense, compact 

 structure. The wide-lumened cells or cell fusions may become so conspic- 

 uous that they appear like larger or smaller pores cut-through "vessels" 

 and according to whether such pores occur, whether they are<iound dis- 

 tributed more or less evenly throughout the annual ring or whether they 

 are more or less distinctly grouped in the spring-wood, the distinction is 

 made into non-porous, diffuse porous, and ring porous woods. 



The ring porous woods, like the oaks, ash, elm, concentrate their large- 

 lumened vessels or "pores" into the spring-wood so that each ring is prom- 



