352 



FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



l!A,N(iK OK VAI.I'KS FOR WKKillT AND STRENGTH. 



Althougli the range of values for the individual tree of any given species varies from butt to top and from 

 center to pcripbery by !."> to -5 per cent and occasionally more, the deviation from average values from one individual 

 to another is not usually as groat as lias been believed; thus of 56 trees of long-leaf pine, -\'2 trees varied in their 

 average 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 of 

 the stem and excluding knots and other defects, gives a more perfect idea of the range of these values: 



Kumje of spii-ifn: trriyJit with aye (kiln-dried irooil). 

 [To avoid IVactioim the values arc multiplied by 100.] 



Though occasionally some very exceptional trees occur, especially in loblolly and short leaf, the range on the 

 whole is generally within remarkably narrow limits, as-appears from the following table: 



Banye of specific weight In trees of the same aye approximately; averages for whole trees. 

 [Specific gravity multiplied by 100 to avoid fractions.] 



From this table it would appear that single individuals of one species would approximate single individuals of 

 another species so closely that the weight distinction seems to fail, but in large numbers for instance, carloads of 

 material the averages above given will prevail. 



INFLUENCE OF LOCALITY. 



In both the Cuban and long-leaf pine the locality where grown appears to have but little influence on weight 

 or strength, and there is no reason to believe that the long-leaf pine from one State is better than that from any 

 other, since such variations as are claimed can be found on any 40-acre lot of timber in any State But with loblolly, 

 and still more with short leaf, this seems not to be the case. Being widely distributed over many localities different 

 in soil and climate, the growth of the short-leaf pine seems materially influenced by location. The wood from the 

 Southern coast and Gulf region, and even Arkansas, is generally heavier than the wood from localities farther north. 

 Very light and line-grained wood is seldom met near the southern limit of the range, while it is almost the rule in 

 Missouri, where forms resembling the Norway pine are by no means rare. The loblolly, occupying both wet and 

 dry soils, varies accordingly. 



INFLUENCE OF MOISTURE. 



This influence is among the most important; hence all tests have been made with due regard to moisture 

 contents. Seasoned wood is stronger than green and moist wood. The difference between green and seasoned wood 

 may amount to 50 and even 100 per cent. The influence; of seasoning consists in (1) bringing by means of shrinkage 

 about 10 per rent more fibers into the same square inch of cross section than are contained in the wet wood; (2) 

 shrinking the cell wall itself by about 50 per cent of its cross section, and thus hardening it, just as the cow skin 

 become^ thinner and harder by drying. 



In the following tables and diagram this is fully illustrated. The values presented in these tables and 

 diagrams are based on large numbers of tests and are fairly safe for ordinary use. They still require further 

 revision, since the relations to density, etc., have hud to bo neglected in this study. 



