134 TIMBER PINES OF THE SOUTHERN UNITED STATES. 



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

 in an op])Osite manner; it is wider in young and thrifty than in okl and stunted trees, and widest 

 along the greatest radius of any section ; similarly, it is wider in the faster-growing Loblolly, Cuban, 

 and Spruce i^ines than in the slow growing Longleaf. 



Besides 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 cut; that of the heartwood 

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

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

 the sapwood contained only (1.2 per cent of turpentine and 1 per cent of rosin, while the heart 

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

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

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

 seasoned, more hygroscopic and subject to relatively greater shrinkage than the heart. This 

 capacity for taking up water readily is probably one of the reasons why sapwood 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 protoplasm and reserve food materials 

 which are rcadilj' seized upon by fungi which 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 made, 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 sa])woo(l of old logs, such as supjily 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 product of 

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

 sai)wood is practically 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 

 insignificant in amount, and their true nature, especially the processes 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 require confirmation. 



ANNUAL RINGS. 



The layers of growth, known and ai)pcaring on any cross section as annual rings, show very 

 distinctly in the wood of these pines. 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 iieriod of most rajiid 

 growtli in height: then they grow more and more narrow toward the jieriphery. In the last sixty 

 toone hundi'ed 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 upjier 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 

 oi' young trees; in old and also in stunted trees it is smaller, since in these the upper portions do 

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



Kings over half an inch wide arc frequently seen in Loblolly and occur in Spruce I'inc; rings 

 one-lbuith of an inch in width occur in veiy thrifty sai)lings ot ail five s])e(ies, but the average 

 width of the rings for sapling timber is usually less than one fotirlh of :m inci). conunoul.\ one-eighth. 

 In trees over one hundred years old it drops to one-twel It h of an inch and cmmi hclow. Tlie average 

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

 (See also tables and diagrams of rate of growth in the introduction, as well as in the several 

 m()nogra])lis.) 



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

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



