226 FIRST BOOK OF FORESTRY 



almost impossible. In maple, cypress, ash, yellow poplar, 

 and many other woods, the surface of the log often is not 

 smooth, but has many little projections (cypress) or depres- 

 sions (maple, etc ), which continue from year to year, i.e., 

 they do not fill up, and one layer of wood after another has 

 the dent at the same point. Similarly, the fibers often run 

 wavy, as shown in the figure. Now if such wood is cut by 

 the saw in a straight line, the darker summer wood in 

 cypress, or the fibers cut almost transversely in maple and 

 other similar woods, appear at this point as a circle of dark 

 on a field of lighter colored wood, and we have the bird's- 

 eye structure. " Curly " maple is wood in which the fibers 

 run in wavy lines, so that part of the fibers are cut across, 

 others cut lengthwise, thus giving bands of darker and 

 lighter shades owing - to the darker color of the cross 

 section. 



Knots. The position of the grain and the appearance 

 of knots are explained by Fig. 85. 



Knots, like cross grain, are normal defects, and occur 

 in all kinds of trees and nearly all kinds and grades of 

 lumber. A dead knot, of course, is always much more 

 serious, since it may drop out at any time and leave a 

 hole in the structure. 



