38 



WOOD AND FOREST. 



the trunk itself close tighter and tighter around it, until it is broken 

 off. Then, unless it has begun to decay, it is successively overgrown 

 by annual layers, so that no sign of it appears until the trunk is cut 

 open. A large trunk perfectly clean of branches on the outside may 

 have many knots around its center, remnants of branches which grew 

 there in its youth, as in Fig. 34, and Fig. 8, p. 18. The general ef- 



Fig. 32. Figure Formed by Pith Rays 

 in Oak (full size). 



Fig 33. Sweet Gum, Showing- Uneven 

 Deposit of Coloring Matter (full size.) 



feet of the presence of a knot is, that the fibers that grow around and 

 over it are bent, and this, of course, produces crooked grain. 



Following are the designations given to different knots by lumber- 

 men: A sound knot is one which is solid across its face and is as 

 hard as the wood surrounding it and fixed in position. A pin knot 

 is sound, but not over y^" in diameter. A standard .knot is sound, 



