li3G 



TIMBER PINES OF THE SOUTHERN UNITED STATES. 



distinguish the real chiiracter oC the tissues, as described later ou. A more serious difficulty 

 arises 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 eases, due to various causes, are too rare to seriously interfere in 

 the establishment of the age of a tree. 



SPRING AND SUMMER WOOD. 



The difference between spring and summer wood is strongly marked iu these pines, the 

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

 appearance of two sharply dertned bands. (See figs. i;5 and 18 ]i.) 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 tJian half as much as the darker summerwood, Avith 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.) 



t-LAST S0-^-2Np 50 RlNGS.-]f- 35P 50 RINGS.' f 4™ 50 RINGS. fcENTRAL 28 RINGS.!! 



irings or 50 

 Iyrs growth,' 



iSUMMER WOOD.I 

 J2%. ' 



SUMMER WOOD 

 30%. 



SUMMER WOOD. 

 45%. 



SUMMER WOOD. 

 52%. 



SUMMER WOOD. 

 46% 



I 



Fig. 13.— Variation of HiiiumiTwood per cent from jiitli to l):irk. 



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

 diagram, fig. 15), i. e., the wider the ring the with'r tlie summcrwooil band. It decreases in a cross 

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

 to the toj) of the tree. Where the growth of the stem is very eccentric, the wood along the greater 

 radius has the greatest prni.ovtion of summeiwood ; thus, in a disk of Longleaf, for instance, there 

 is on the north .side a radius of 15l2 mm. with 'J7 \)cv cent summerwood; on the south side a radius 

 of its 111111. and a summerwood ])er cent of only 20 per cent. In the .stumi> section the great 

 iriegiilarity in the coiitdur of tiie rings is ac<'omi>aiiicd 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 a greater i)art of thecoar.se grained wood which was grown while the tree was young 

 than in the fine-ringed outer parts of the log, grown in the (dd age period. It also forms a greater 

 part ill the volume of the butt than of the top log, and thus fully exiilainsthe well known ditlVience 

 in the weight, strengtii, 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 llnlirs below refer to 

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



