DESCRIPTION OF WOOD. 53 



THE WOOD. 1 



The wood of the Longleaf Pine is heavier and stronger than that of any other pine offered in 

 the market. The average weight of the kiln-dry wood is about 38 pounds, that of the lumber where 

 the outer lighter portion of the log is largely cut away about 40 pounds, per cubic foot. The 

 kiln dry wood of the butt weighs about 45 pounds per cubic foot; that of a log 50 to 60 feet from 

 the ground only about 33 pounds, a decrease of weight (and with it of strength) of about 25 per 

 cent. Similarly the wood of inner portions of a log are 15 to 20 per cent heavier than those of the 

 outer portions; or, in other words, the wood laid on when the tree is young is heavier than that 

 laid on when it is old, quite contrary to the common belief which seems to associate the light 

 sapwood color of the young sapling with inferior material. The wood shrinks about 10 per cent of 

 its volume in drying, about 6 to 7 per cent along the rings (tangentially) and 3 to 4 per cent along 

 the radius; seasons easily and without great injury. As in other pines, the greatest amount of 

 water is contained in the sapwood, varying from 30 to 50 per cent of the weight of the fresh wood, 

 while the heartwood contains but about 20 per cent. 



In its stiffness and strength the wood is remarkable. The average of a great number of tests 

 indicates for the dry wood of Longleaf Pine an elasticity of 1,540,000 pounds per square inch; 

 strength in cross breaking, 10,900 pounds per square inch ; strength in compression, 6,850 pounds 

 per square inch; strength in tension, 15,200 pounds per square inch; strength in shearing, 706 

 pounds per square inch. 



In its structure the wood of the Longleaf Pine resembles that of the other Southern pines. 

 Sapwood and heartwood are well defined; on the fresh cross section the former is light yellowish 

 white, the latter a yellowish brown ; drops of limpid resin ooze from every resin duct in the sap- 

 wood, the surface of the heartwood remains dry (exceptions only in "lightwood"). The sapwood 

 contains much more water, but is far less resinous than the heartwood. This latter contains 5 to 

 10 per cent of resin (1 part turpentine to 15 to 20 parts resin), while in the former the resin 

 rarely exceeds 2 per cent. If not kiln-dried, fresh sapwood rapidly "blues" on exposure; heart- 

 wood does not, and in general excels the sapwood in durability. On drying, the sapwood shrinks 

 more than the heartwood of the same weight. Contrary to common belief, the wood substance, or 

 cell wall, is not increased in the change from sapwood to heartwood, the walls do not grow thicker, 

 the cavities of the cells do not fill up with foreign matter, nor does the strength of the wood seem 

 to be increased by the change. In general the width of the sapwood is greatest in young and 

 thrifty trees, grows smaller in old and stunted trees, is greatest in the lower parts of the stem and 

 smaller in the top and branches. In old logs the sapwood is made up of from 70 to 100 rings, 

 showing that the wood of any one ring remains in older trees seventy to one hundred years in the 

 sapwood condition before it changes to heartwood. In young trees this period is much shorter, 

 twenty-five to forty years commonly sufficing for thrifty trees at the age of sixty to seventy years, 

 but in stunted individuals it is materially prolonged. The share of the sapwood in the total volume 

 of the stem is always considerable; even in typical old trees of this species it forms 40 per cent 

 and more, while thrifty stems under one hundred years are practically all sapwood. 



The annual, or yearly, rings are clearly defined ; they are widest near the pith and grow rather 

 uniformly narrower toward the bark. In the inner part a width of one-twelfth of an inch is quite 

 common ; the rings near the bark of old logs usually measure less than one twenty fifth of an inch, 

 often scarcely one fiftieth of an inch. For old trees the average widtli for the entire stem may be 

 set at about one twentieth to one-twenty-fifth of an inch. Each ring consists of two well-marked 

 parts, an inner, softer, whiter part, the springwood, and an outer, harder, and darker portion, the 

 .summerwood, so called because formed during the latter part of the growing season. 



The amount of the summerwood in each ring differs in different parts of the tree. It forms 

 about 45 per cent of the volume of all the wood of the stump, and only about 24 per cent of the 

 wood 60 feet from the butt. It is greater in the heavy inner part of an old log than in the lighter 

 outer portion*, and being of a darker color furnishes a convenient means of distinguishing heavy 

 wood. In its finer anatomy (histology) the wood resembles that of the other pines of the fa-da 

 group. (For the details of structure see the comparative study by Mr. Roth appended to these 

 monographs.) 



'This st:itfini-nt is furnished by Mr. Filiburt Koth, in charge of timber investigations in the Division of Forestry. 



