48 ECONOMIC WOODS OF THE UNITED STATES / 



/ 

 the opposite condition, such as is common La all prominently 

 ring-porous woods (Frontispiece; Plate III), (e.g., Quercus, Cas- 

 tanea, JJlmus, Fraxinus), and in other woods with decided differ- 

 ences between early and late wood {e.g., Pinus -palustris, P. tceda, 

 and Pseudotsuga). 



Texture and grain are terms very commonly confused in 

 popular usage. The distinctions as above expressed will obviate 

 the difficulty. resulting from the attempt to make the term "grain" 

 too comprehensive. 



Reference 



Record, S. J.: Grain and Texture in Wood, Forestry Quarterly, Vol. IX, 

 No. 1, 1911, pp. 22-25 (reprinted in Woodcraft, June 1911). 



KNOTS 



Branches originate, as a rule, at the central axis of a stem and, 

 while living, increase in size by the addition from year to year 

 of woody layers which are a continuation of those in the stem. 

 From this it follows that the form of the included portion or knot 

 approaches that of a cone with its apex inward. 



During the development of a tree most of the limbs, especially 

 the lower ones, die, but persist for a time — often for a great many 

 years. Subsequent layers of growth of the stem are not intimately 

 joined with the fibres of the dead limb, but are laid around its 

 base. Hence dead branches produce loose knots which may drop 

 out after the tree has been cut into lumber. 



The stubs of dead limbs that have broken off are usually 

 occluded by subsequent growth so that the outer surface of the 

 bole is smooth or clear, especially toward the butt. The interior 

 of all stems is more or less knotty, but in butt logs the knots 

 are fewest and smallest. Sometimes knots enhance the value of 

 timber for cabinet work and interior finish, by giving it a pleasing 

 figure. Material cut near the junction of a large limb or at the 

 base of a crotch usually exhibits very handsome grain. 



Knots materially affect checking and warping, ease in working, 

 and cleavability of timber. They are defects which weaken timber 

 and depreciate its value for structural purposes where strength is 

 an important consideration. The weakening effect is much more 

 serious where timber is subjected to bending and tension than 

 where under compression. The extent to which a knot affects 

 the strength of a beam depends upon its position, size, direction 



