22 



TIMBER. 



is not, so that in this latter case the distinction depends chiefly on hard- 

 ness, and in the former on an accidental case of slow or rapid growth. 

 Generally the direction of the wood fibers is parallel to the axis of 

 the stem or limb in which they occur, the wood is straight grained, but 



Fig. 11.— Spiral grain. 

 Season checks, after re- 

 moval of bark, indicate 

 the direction of the fibers 

 or grain. 



barK 



Fig. 12.— Alternating spiral grain in cypress. Side 

 and end view of same piece. When the bark was 

 at o the grain at this point was straight. From 

 that time each year it grew more oblique in one 

 direction, reaching a climax at a, and then turned 

 back in the opposite direction. These alterna- 

 tions were repeated periodically, the bark sharing 

 in these changes. 



■i.ft. 



in many cases the course of the fibers is spiral or twisted around the 

 tree as shown in fig. 11, and sometimes (commonly in butts of gum 

 and cypress) the fibers of several layers are oblique in one direction, 

 and those of the next series of layers are oblique in the opposite 



direction, as shown in fig. 12; the wood is 

 cross or twisted grained. Wavy grain in a 

 tangential plain as seen on the radial section 

 is illustrated in fig. 13, which represents an 

 extreme case observed in beech. This same 

 form also occurs on the radial plain, causing 

 the tangential section to appear wavy or in 

 transverse folds. When wavy grain is fine, 

 i. e., the folds or ridges small but numerous, 

 it gives rise to the " curly " structure fre- 

 quently seen in maple. Ordinarily, neither 

 wavy, spiral, nor alternate grain is visible 

 on the cross section; its existence often escapes the eye even on smooth, 

 longitudinal faces in sawed material, so that the only safe guide to 

 their discovery lies in splitting the wood in the two normal plains. 



Generally the surface of the wood under the bark, and therefore also 

 that of any layer in the interior, is not uniform and smooth, but is 



Fig. 13. — Wavy grain in beech; 

 after Nordlinger. 



