THE WOOD 



225 



Some cells in wood are large enough to be seen with 

 the unaided eye, but most of them are very small and 



FIG. 84. Wavy Grain in Beech 

 (After Nordlinger) 



can be seen only if much magnified. 

 If the fibers run straight up and 

 down in the log, so that it splits 

 straight, we call it straight grain; 

 if they run spirally around as well 

 as up, we call it spiral or twisted 

 grain. Most logs have more or 

 less twisted grain. Sometimes the 

 fibers twist one way in a number 

 of rings and then in the opposite 

 way in the rings farther out (see 

 Fig. 82), and thus make splitting 



FIG. 85. Section of Knot 



P, pith of both stem and limb ; 

 1-7, seven yearly layers of 

 wood ; a, 6, knot or basal part 

 of a limb which lived four 

 years, then died and broke off 

 near the stem, leaving the 

 part to the left of a, 6 a 

 " sound " knot, the part to 

 the right a " dead " knot, 

 which would soon be entirely 

 covered by the growing stem 



