"curly" 



AND 



"bird's-eye" 



GRAIN. 



23 



channeled and pitted by numerous depressions which differ greatly in 

 size and form. Usually, any one depression or elevation is restricted 

 to one or few annual layers (i. e., seen only in one or few rings) and is 

 then lost, being compensated (the surface at the particular spot evened 

 up) by growth. In some woods, however, any depression or elevation 

 once attained grows from year to year and reaches a maximum 

 size which is maintained for many years, sometimes throughout life. 



In maple, where this tendency to preserve 

 any particular contour is very great, the 

 depressions and elevations are usually small 

 (commonly less than one-eighth inch), but 

 very numerous. On tangent boards of such 

 wood the sections of these pits and promi- 

 nences appear as circlets and give rise to the 

 beautiful "bird's-eye" or "landscape" struc- 

 ture. Similar structures in the burls of 

 black ash, maple, etc., are frequently due to 

 the presence of dormant buds, which cause 

 the surface of all the layers through which 

 they pass to be covered by small conical 

 elevations, whose cross sections on the sawed 

 board appear as irregular circlets or islets 

 each with a dark speck, the section of the pith 

 or "trace" of the dormant bud in the center. 



In the wood of many broad- leaved trees 

 the wood fibers are much longer when full 

 grown than when they are first formed in the 

 cambium or growing zone. This causes the 

 tips of each fiber to crowd in between the 

 fibers above and below, and leads to an 

 irregular interlacement of these fibers, 

 which adds to the toughness but reduces the 

 cleavability of the wood. 



At the junction of limb and stem the fibers 

 on the upper and lower sides of the limb 

 behave differently. On the lower side they 

 run from the stem into the limb, forming an 

 uninterrupted strand or tissue and a perfect 

 union. On the upper side the fibers bend aside, are not continuous 

 into the limb, and hence the connection is imperfect (fig. 14). 



Owing to this arrangement of the fibers, the cleft made in splitting 

 never runs into the knot, if started on the side above the limb, but is 

 apt to enter the knot if started below, a fact well understood in wood 

 craft. When limbs die, decay, and break off, the remaining stubs are 

 surrounded and may finally be covered by the growth of the trunk, and 

 thus give rise to the annoying "dead" or "loose" knots. 



Fig. 14.— Section of wood showing 

 position of the grain at base of a 

 limb. P, pith of both stem and 

 limb; 1-7, seven yearly layers of 

 wood ; a, h, 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. 



