i4f; 



TIMBER PINES OF THE SOUTHERN UNITED STATES. 



distinguish the real character of the tissues, as described hiter on. A more serious difficulty 

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

 three cells (see fig. 18) and occasionally disappears, i. e., is entirely wanting in some parts of the 

 cross section. Generally these cases, due to various causes, are too rare to seriously interfere in 

 the establishment of the age of a tree. ^ 



.SPRING AND STTM:MER WOOD. 



The difference 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 figs. 13 and 18 U.) 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 nuich as the darker summerwood, with a specific gravity of 

 about 0.90 to 1.05, so that the weight and with it the strength of the wood is greater the larger 

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



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

 diagram, fig. 15), i. e., the wider the ring the wider the summerwood 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 top of the tree. Where the growth of the stem is very eccentric, the wood along the greater 

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

 is on the north side a radius of 152 mm. with 27 per cent summerwood ; on the south side a radius 

 of 98 mm. and a summerwood per cent of only 20 per cent. In the stump section the great irreg- 

 ularity 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 Ibrms a greater i>art of the coarse-grained wood which was grown while the tree was young 

 than in the fine-ringed outer parts of the log, grown in the old-age period. It also 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 i)arts of the tree. Tlie 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 iialivsi below refer to 

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



