WOOD OF SOUTHERN PINES. 107 



The change from sap to heart wood begins earlier in young trees than in the younger portions 

 of older trees ; in these latter, sections thirty-six and forty years old are quite commonly found 

 still entirely made up of sapwood, while in young trees, as stated above, the change begins before 

 the age of thirty years. 



The progress of the transformation is somewhat influenced by the rate of growth; it is slower 

 in slow-growing trees and usually also on the slower-growing radius, i. e., there are more rings of 

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

 in an opposite manner; it is wider in young and thrifty than in old and stunted trees, and widest 

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

 and spruce pines 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 ducts 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 0.2 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 readily seized upon by fungi which cause "bluing" and decay. Such living tissue does 

 not exist in the heartwood. The heartw r ood 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 sapwood of old logs, such as supply 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 

 sapwood 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 oz 

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



ANNUAL RINGS. 



The layers of growth, known and appearing 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 period of most 

 rapid growth in height; then they grow more and more narrow toward the periphery. In the last 

 sixty to one hundred 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 part 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 upper portions do not share in the more rapid growth of the early years. 



Eings 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 saplings of all five species, but the average 

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

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



