202 



INTERLOCKED GRAIN, that is, spiral 

 grain that reverses in direction from 

 right to left and back every few years, 

 is hereditary, because it occurs almost 

 universally in certain species, notably 

 sweetgum, black tupelo, and many of 

 the tropical species. It produces a 

 beautiful ribbon figure in quarter- 

 sawed lumber and quarter-sliced ve- 

 neer, especially in species in which the 

 wood has a high natural luster, such as 

 mahogany, Philippine lauan, and Afri- 

 can sapele. But it also causes lumber, 

 especially plain-sawed boards, to warp 

 in drying, and makes planing difficult, 

 because the knives must cut against 

 the grain in part of the board no mat- 

 ter which way it is planed. Wood with 

 interlocked grain is difficult to split, 

 although for driveway planking and 

 large rollers, such as those used for 

 house moving, that is an advantage. 



Other types of distorted grain that 

 occur in occasional trees are wavy, 

 curly, and bird's-eye grain, all of which 

 are considered ornamental and in- 

 crease the value of the trees in which 

 they are found. Unfortunately, they 

 cannot be detected easily without mu- 

 tilating the young trees, although a 

 limited amount of research indicates 

 that, if the outer bark is removed over 

 a small area of the stem, the pattern 

 of the grain is revealed by the fibers 

 in the inner bark, which follow the 

 same course as the wood fibers. Cut- 

 ting into but not through the inner 

 bark in spots does not damage the tree. 



The profits from growing trees cer- 

 tainly could be increased if wood of 

 desirable types of figure could be pro- 

 duced at will. Apparently successful 

 experiments are being made in Fin- 

 land in growing figured birch. If, as 

 in the case of walnut, a delicious nut 

 with a thin shell could be produced 

 in addition to figured wood, there need 

 be little question as to whether the 

 financial outcome of growing such 

 timber would be plus or minus. Prob- 

 lems of that kind require a great deal 

 of special study for a long period, but, 

 like all research, it need not be re- 

 peated once it is done thoroughly. 



Yearbook of Agriculture 1949 



KNOTS, the most common defects 

 in lumber, are the bases of live and 

 dead branches imbedded in the grow- 

 ing tree trunk. They affect the appear- 

 ance, smoothness, strength, tightness, 

 finishing, and other properties of lum- 

 ber and veneer. Lumber without knots 

 is worth three or four times as much 

 as knotty lumber, except where the 

 knots are such that they are consid- 

 ered ornamental. The parts of knots 

 that are produced by limbs while 

 green, known as intergrown knots, are 

 not so detrimental as those produced 

 by limbs that persist after death, which 

 often are discolored, even partly de- 

 cayed, and loose. 



The development of knots in trees 

 can be reduced in two ways. One 

 way is to maintain stand conditions 

 crowded enough while the trees are 

 young that the lower branches will die 

 and break off while they and the tree 

 trunk are still small in diameter. In 

 such trees the knots in the lower part of 

 the trunk, especially the intergrown 

 parts, as a rule will be shorter. 



The dead branches often persist for 

 an extraordinarily long time in some 

 species, notably eastern and western 

 white pines, sugar pine, red pine, pon- 

 derosa pine, Douglas-fir, and Engel- 

 mann spruce. They may hang on after 

 death for 50 to 150 years or more be- 

 fore they break off, leaving longer 

 dead knots than intergrown knots in 

 the lower portion of tree trunks from 

 stands that are fairly well-stocked. In 

 such species, practically no knot-free 

 lumber can be produced naturally in a 

 commercially reasonable length of 

 time, 75 to 125 years. 



A better way to produce knot-free 

 lumber is to prune young timber trees. 

 Whether it pays to prune forest trees 

 depends on the market value of differ- 

 ent grades of lumber of a particular 

 species when the wood is harvested and 

 on the original cost of pruning and the 

 number of years over which the cost 

 must be carried. But because the dif- 

 ference in value of knot-free and knot- 

 ty lumber from virgin timber is large 

 and unpruned second-growth timber 



