

WOOD OF SOUTHERN PINES. 



109 



one or more, rarely two, dark colored lines, which precede the true summer wood band of the ring. 

 These lines, resembling the summerwood in color and composed like it of think-walled cells, follow 

 the true springwood of the year and are separated from the summerwood and from each other 

 ^if there are more than one) by a light-colored line resembling springwood. While occasionally 

 this is somewhat misleading in counting the rings, a moderate magnification usually suffices to 

 distinguish the real character of the tissues, as described later on. 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 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 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. 17 and 22.) In wide rings the transition 



"--LAST 50-4-21° 50 RINGS.-t 339 50 RINGS. 1 f 4™ 50 RINGS. ^CENTRAL 28 RINGS.*! 



•rings dr sn' 



;yrs. growth. 1 



tSUMMER WOOD. 1 

 22% 



SUMMER WOOD 

 30%. 



SUMMER WOOD. 

 45%. 



SUMMER WO00. 

 52%. 



SUMMER WOOD. 

 46%. 



Fig. 17 — Variation of summerwood per cent from pith to bark. 



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 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 figs. 17 and 19.) 



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

 diagram, fig. 19), 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 

 irrregularity 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. 

 17) ; it forms a greater part 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 



