110 



FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



part in the volume of the butt than of the top log, and thus fully explains the well-known difference 

 in the weight, strength, and value of the various parts of the tree. The following table serves to 

 illustrate this point. The numbers in each line refer to the average values for the same ten annual 

 layers through three sections of the tree at varying height. The figures in italies below refer to 

 specific gravity for the same layer. The values for specific gravity were calculated on the basis of 

 allowing a specific gravity of 0.40 for springwood and 0.90 for summerwood, the values for the 

 entire disks as actually observed being given below : 



Summerwood per cent and specific gravity in various parts of a tree of longleaf pine. 



Rings from periphery. 



Section I, 3 feet from ground. 



Section IV, 35 feet from 

 ground 



to 

 10 



39 



.59 



26 



.53 



Section VII, 70 feet from I 

 ground... 23 



51 



11 

 to 

 20 



44 

 .62 



24 



.52 



16 



48 



21 

 to 

 30 



40 

 .60 



25 



.52 



17 



AS 



31 

 to 

 40 



42 

 .61 



34 



.57 



18 

 .40 



41 

 to 

 50 



38 



.59 



51 

 to 

 60 



35 



.57 



61 

 to 



70 



45 



M 



__ 24 26 



M \ .52 .53 



18 20 

 .49 .50 



10 



71 



81 



91 



to 



to 



to 



80 



90 



100 



32 



44 



66 



.56 



.62 





24 



35 



49 



.52 



.57 



.64 



20 



18 



26 



.50 



.49 



.5;3 



101 

 to 

 110 



43 



.6*1 



31 

 .55 



21 

 .50 



111 



121 



131 



141 



151 



161 



171 



181 



191 



201 



211 



221 



231 



Aver- 



to 



TO 



to 



to 



to 



to 



to 



to 



to 



to 



to 



to 



to 



age 



for 



total. 



120 



130 



52 



140 

 56 



150 



48 



160 



170 



ISO 

 43 



190 

 47 



200 

 47 



210 

 52 



220 

 45 



230 



236 

 al5 



43 



46 



48 



45 



.61 



.66 



.68 



.04 



.63 



.64 



.61 



.63 



.63 



.66 



.62 



.61 



.47 



. 625 



33 



43 



34 



40 



31 



34 



33 



33 



31 



■ 22 



66 







29 



.56 



.61 



.57 



.60 



.55 



.57 



J)6 



.56 



.55 



.51 



■AS 











.545 



9A 



19 



.49 



39 



.49 



22 

 .,51 



16 



.48 



18 



.4.9 



e2 



.41 















18 



■M 



















. 450 















a Six rin^s next to pith. h Two rings- 



The observed values of specific gravity for the three sections are 0.700, 0.560, and 0.490, respectively. 



e One ring. 



It will be noticed that the greatest difference between the calculated and the actual value of 

 specific gravity occurs in the section at the stump. This is fully accounted for by the fact that 

 large amounts of resin, not considered in the values of summerwood per cent, always occur in 

 this portion, adding from 5 to 20 per cent to the weight of the wood. 



100 



Decades of Rings from periphery 



Fig. 18— Variation of specific gravity with summerwood per cent and age of section in longleaf pine, the solid lines referring to a section 3 

 feet from the ground, the dotted lines to one 14 feet from the ground. (Specific gravity as actually observed on pieces of 1 inch radia 

 extent.) 



In stunted trees the summerwood forms nearly as great a per cent of the total volume for the 

 whole tree as in thrifty trees of the same age, but in the stunted growth, or extremely narrow 

 ringed portion of otherwise normal trees, the per cent of summerwood is markedly decreased, a 

 feature which becomes conspicuous in the lighter color of the wood of such portions. (See diagram, 

 fig. 22, A.) Where, on the other hand, the rate of growth in an old tree is suddenly increased by 

 the accessibility of more light, for instance, the summerwood per cent also is disproportionately 

 increased, but this disproportion appears to be more transient, i. e., a decrease in the summerwood 

 per cent sets in sooner than for the rate of growth or the width of the rings. (See fig. 10.) In 

 some of the rapidly grown loblolly and spruce pine the summerwood forms but a small part of the 



