134 TIMBER PINES OF THE SOUTHERN UNITED STATES. 



sapwood. The width of the sapwood, on the other hand, stands in rchitioii to the rate of growth 

 ill an opjxisite manner: it is wider in younrf and thrifty tlian in old and stunted trees, and widest 

 aloiif; Ilif greatest radius of any seetion ; similarly, it is wider in the faster growing Loblolly, Cuban, 

 and Spruee pines than in the slow growing Longleaf. 



ISesides being of a lighter color the sapwood differs from the heartwood in several respects. 

 Its resin is limpid and oozes out of the pores or resin duets of any fresh eut; that of the heartwood 

 does not flow, except in rare cases, Iroiii saturated pieces or "light wood." The sapwood coiitaius 

 much less rosin — both rosin and turpentine — than the lieart wood. Thus in a .section of Longleaf 

 the sai>wood containeil only 0.2 per cent of turpentine and 1 per cent of rosin, while the heart 

 contained from 2 to 4 ])er cent of turpentine and 12 to 24 per cent of rosin, and though this is an 

 extreme case the heart generally has three to tive times as much resinous matter as the sap. The 

 fresh sapwood contains three to five times as much free water as the heartwood and is, even when 

 seasoned, moie hygroscopic and subject to relatively greater sliriiikage than the heart. This 

 capacity for taking up water readily is probably one of the reasons why sai)wood decays more 

 readily. In addition, the parenchyma cells of the medullary rays and resin ducts (see further on) 

 contain, at least in the outer parts of the sapwood. living ])roto])lasm and reserve food materials 

 which are readily seized upon by fiuigi wliicli cause ''bluing'" and decay. Such living tissue does 

 not exist in the heartwood. The heartwood in old logs generally is heavier than the sapwood. 

 This is not due to any later thickening or growth of its cell walls, after their original formation, 

 but is due chiefly to two causes: 



1. The heartwood of old logs was formed when the tree was younger, and iiia<l(', naturally, 

 heavier wood. 



2. The accumulation of resin in the heart already referred to increases often very considerably 

 the weight of the heartwood. 



In the same way the sapwood of old logs, such as supjdy the sawmills, is weaker than the 

 heartwood of the same logs, but this is not because the wood is in the sapwood condition, but 

 because it is lighter and its summerwood per cent smaller, being, as stated before, the jiroduct of 

 old age when heavy and strong wood is no longer formed. Chemically the wood substance of 

 sapwood is jiractically like that of heartwood; the coloring substances which permeate the cell 

 walls in heartwood appear to be infiltrations, i. e., deposited in the walls from solutions; they are 

 insigniticant in amount, and their true nature, especially the i)rocesses leading to their formation, 

 are not yet fully understood. The most modern views which consider these coloring bodies or 

 heartwood substances as products of oxidation of tannin still reiiuire confirmation. 



ANNUAL RINGS. 



The layers of growth, known and appearing on any cross section as animal rings, show very 

 distinctly in the wood of these iiines. In a section 8 or 10 feet from the ground the rings are 

 widest at the center, of considerable width for the first thirty to fifty rings, the ])eriod of most rapid 

 growth in height: then they grow more and more narrow toward the periphery. In the last sixty 

 to one huiidrtid rings of very old logs the decrease is very small, the rings remaining practically of 

 the same width. The same year's growth is usually wider in the upper i)art of the stem, both in 

 young and old trees, but the average width of the rings is naturally greater in the upper part only 

 of young trees; in old and also in stunted trees it is smaller, since in these the upjier portions do 

 not share in the more rajiid growth of the early years. 



Kings over half an inch wide are frequently seen in Loblolly and occur in Spruce Pine; rings 

 one-fourth of an inch in width occur in very thrifty sa[)lings of all five species, but the average 

 width of the rings for sapling timber is usually less than one fourth of an iiicii, cominonlv one-eighth. 

 In trees over one hundred years old it drops to one-twelfth of an inch and even below. The average 

 width of the rings is normally smallest in Longleaf Pine, being onctwenty-tifth of an inch and less. 

 (See al.so tables and diagrams of rate of growth in the introduction, as well as in the sevei-al 

 monogra]ihs.) 



The intiuence of orientation on the width of the rings is completely obscured by other, more 

 potent influences, so that sometimes the radms on the north side, other times that of some other 



