146 



IIMIIKK 1MNKS OK THE SOUTHERN TNITED STATES. 



distinguish tin- real diameter of the tissues, as described later on. A more serious dillieulty 

 arises in very old, slowly growing trees, where the ring sometimes is represented by only one to 

 three cells (see fig. !"*) and occasionally disappears, i. e., is entirely wanting in some parts of the 

 cross section, (ienerally these cases, due to various causes, are too rare to seriously interfere in 

 the establishment of the age of a tree. 



SPRING AND SUMMER WOOD. 



The dilVereiice between spring and summer wood is strongly marked in these pines, the 

 transition from the former to the latter being normally abrupt and giving to the annual ring the 

 appearance of two sharply defined bands. (See tigs. J.'! and 1815.) In wide rings the transition is 

 sometimes gradual. The springwood is light colored, has a specific gravity of about 0.40. and thus 

 weighs somewhat less than half as much as the darker sumnierwood, with a specific gravity of 

 about O.'.IO to 1.0."), so that the weight and with it the strength of the wood is greater, the larger 

 the amount of stimmerwood. (See diagram, fig. 14.) 



t-LAST 50-4- 2i 50 RINGS.-i- 3?S 50 RINGS. f 4 50 RINGS. ^CENTRAL 28 RINGS)! 



'RINGS OR 50 



|YRS GROWTH' 



iSUMMER WOOD. 1 SUMMER WOOD. I 



22%. 30%. | 



SUMMER WOOD. 

 45%. 



SUMMER WOOD. 

 527.. 



SUMMER WOOD. 

 167.. 



Flo. 13. Variation of Buninicrwood per cent from pith to bark. 



The absolute width of the sumnierwood varies generally with the width of the ring (see 

 diagram, fig. 15), i. e., the wider the ring the wider the sumnierwood band. It decreases in a cross 

 section of an old log from near the pith to the periphery, and in the same layer, from the stump 

 to the toj> of the tree. Where the growth of the stein is very eccentric, the wood along the greater 

 radius has the greatest proportion of summerwood; thus, in a disk of Longleaf, for instance, then- 

 is on the north side a radius of 15i> mm. with 27 per cent summerwood; on the south side a radius 

 of 08 mm. and a summerwood per cent of only -'() per cent. In the stump section the great 

 irregularity in the contour of the rings is accompanied by a corresponding irregularity in the 

 outline of the summerwood. 



The summerwood generally forms less than half of the total volume of the whole log (see fig. 

 13); it forms ;v greater part of the coarse grained wood which was gr>wn while the tree was young 

 than in the line-ringed outer parts of the log, grown in the old age period. It ;ilso forms a greater 

 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 itxlicx below refer to 

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



