Report upon the forestry investigations of the of agriculture1877-1898 . hen over , with amaximum of at tlie age of 30 to 40. The average weightfor old trees ( to ) lies about the seventy-fifth year,the weight then falling olf to about at the age of 140,and continuing to decrease to below as the trees growolder. That these statements refer only to the clear portions ofeach log, and are variably affectcd at each whorl of knots (every10 to 30 inches) according to their size, and also by the variableamounts of resin (up to 20 per cent of the dry weight), m
Report upon the forestry investigations of the of agriculture1877-1898 . hen over , with amaximum of at tlie age of 30 to 40. The average weightfor old trees ( to ) lies about the seventy-fifth year,the weight then falling olf to about at the age of 140,and continuing to decrease to below as the trees growolder. That these statements refer only to the clear portions ofeach log, and are variably affectcd at each whorl of knots (every10 to 30 inches) according to their size, and also by the variableamounts of resin (up to 20 per cent of the dry weight), mustbe self-evident. Sapwood is not necessarily weaker than heartwood, onlyusually the sapwood of the large-sized trees we are now usingis represented by the narrow-ringed outer part, which wasformed during the old-age period of growth, when naturally lighter and weaker wood is made; but the wood formed during the more thrifty diameter growth of the firsteighty or one hundred years—sapwood at the time, changed into heartwood later—was, even as sapwood, theheaviest and 200 20 eo so C EO 6ff JBO SOO SCALE VEffr/CAl ^ /Er. w/f/zo/vrAi /sw ?=///!/. Fig. 92.—Schematic section through atom of long-leaf pine,sbowiug variation of specific weight, with height, diame-ter, and age, at 20 {.aba), CO (dcd), 120 (race), 20O (////)years. 352 FOEESTEY INVESTIGATIONS U. S. DEPAETMENT OP AGRICULTURE. KANGE OF AALUES FOR WEIGHT AND STRENGTH. Although the range of values for the iudlvidual tree of any given species varies from butt to top and fromcenter to periphery by 15 to 25 per cent and occasionally more, the deviation from average values from one individualto another is not usually as great as has been believed; thus of 56 trees of long-leaf pine, 42 trees varied in theiraverage strength by less than 10 per cent from the average of all 56. The following table of weight (which is a direct and fair indication of strength), representing all the wood ofthe stem and excluding
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectforestsandforestry
