The Growth of Stems 155 



(i) Ring-porous woods have larger and more numerous tra- 

 cheae in the spring wood, and denser summer wood. To 

 this class belong ash, catalpa, locust, elm, chestnut, oak, 

 and hickory. 



(2) Diffuse-porous woods have the pores about equally dis- 



tributed through both spring and summer wood, and 

 annual rings inconspicuous. Here belong walnut, 

 cherry, cottonwood, beech, maple, holly, birch, gum, 

 and basswood. 



(3) Non-porous woods may have conspicuous rings when the 



wood cells, or tracheids, are large and thin walled in the 

 spring wood, and smaller and heavier walled in the 

 summer wood. Yellow pine and hemlock exemplify this 

 type. Red cedar, spruce, and arbor vitae have incon- 

 spicuous rings, marked only by the slight decrease in 

 size of cells near the outer edge of the ring. Some of the 

 non-porous woods have prominent resin ducts ; in 

 others ducts are wanting.^ 



Structure determines usefulness. For manufacturing pur- 

 poses the differences in wood structure just outlined are of the 

 greatest importance, because the quality of the products is largely 

 a matter of wood structure. Spruce, because of its soft texture 

 and freedom from resin, is used for paper pulp. Its uniform 

 grain makes it desirable for sounding boards of musical instru- 

 ments and in the manufacture of airplanes. Walnut, because of 

 its color and the ease with which it may be polished, is prized for 

 gunstocks and furniture. Hickory is the best wood for tool 

 handles and the spokes and rims of wheels. Oak is valuable for 

 flooring, interior finish, and furniture. Cypress and redwood are 

 especially noted for their durability in the soil or under conditions 

 where other woods decay. Ash is notably strong, elastic, and 



^ Further information on the identification of woods may be obtained from 

 Guidebook for the Identification of Woods Used for Ties and Timbers (United States 

 Forest Service). 



