Heartwood inner

Woody material, the most important part of mature trees, which is differentiated into sapwood (outer region), where the sap migrates from roots to leaves and heartwood (inner region) that is no longer used for sap transport, which exists only when the stan, at that height, is old enough... 

Just under the bark of a tree is a thin layer of cells, not visible to the naked eye, called the cambium. Here, cells divide and eventually differentiate to form bark tissue outside of the cambium and wood or xylem tissue iaside of the cambium. This newly formed wood on the iaside contains many living cells and conducts sap upward ia the tree, and hence, is called sapwood. Eventually, the inner sapwood cells become iaactive and are transformed iato heartwood. This transformation is often accompanied by the formation of extractives that darken the wood, make it less porous, and sometimes provide more resistance to decay. 

Studies on Pinus species have shown that the nature and amount of extractives depend upon the percentage of heartwood present and thus on tree age. In Piims radiata, heartwood starts forming once the trees are about 12 to 15 years old. Heartwood extractives occur in greatest amount in inner growth rings near the pith (Uprichard, 1971 Lloyd, 1978) especially in the butt log of mature trees (Table 2.5). The high level of resin in the inner zone appears due to a process of enrichment with sapwood extractives via the transverse resin canals (Harris, 1965). Resin acids predominate in heartwood and comprise from 70-80% of total extractives, however in sapwood there are approximately equal amounts of resin acids and fatty acids (Table 2.6). An important feature of the resin constituents of pines is that a mixture of resin acids in turpentine occur in the resin canals, and the fatty acid esters and unsaponifiable materials occur in the ray parenchyma resin. In some processes, for example refiner mechanical pulping some separation of these chemical components can occur. 

In Leslie Taylor s section concerning pan d arco, there are comments that adulteration or substitutions are often made. Thus, a main anticancer constituent is the compound lapachol, which may be in concentrations of 2 to 7% in true pau d arco, whereas other related species may have none. Moreover, in the chemical analysis of 12 commercially available products, only 1 showed even trace amounts. Either substitutions had been made, or there was degradation during processing, transport, and storage. And whereas most research studies have been confined to the heartwood, most commercially available products contain the inner and outer bark of the tree, which is stripped at the sawmills from the ten or so species that are logged. The call is for standardized extracts that guarantee the lapachol and naphthoquinone content. 

To summarize, the analytical information of archaeological or ancient wood shows variability in chemical changes and losses that may result from the burial environment, the wood species, sapwood or heartwood, outer or inner wood, anomalies in growth, and certainly the methods of analysis. The stability of wood biopolymers has been found to be (in decreasing order) lignin, pectin, cellulose, and hemicellulose. As a rule, increase in moisture content indicates increase in degradation. 

Much of the research related to pau d arco has been done on the compound lapachol, which is reported by one reference to be present in the heartwood at a concentration of 2 to 7%, with less in the bark (Taylor 2005). An analysis of commercial pau d arco wood and bark products, however, indicated that the lapachol content in the wood was 0.001%, with no lapachol detected in bark products (Awang et al. 1994). Similarly, no lapachol was identified in an aqueous extract of pau d arco inner bark (Steinert et al. 1996). Publications... 

Figure 16.1. Detailed wood structure Cross section of white oak tree trunk a. outer bark (dry dead tissue) b. inner bark (living tissue) c. cambium d. sapwood e. heartwood f. pith g. wood rays. From U.S. Department of Agriculture (1999) Wood Handbook Wood as an Engineering Material. USDA Forest Products Society, Madison, WI and reproduced with permission.

Timber is classified as hardwood and softwood. Hardwood comes from the broadleaved trees such as oak, maple, and ash. Softwood is the product of coniferous trees such as pine, birch, spruce, and hemlock. The terms hardwood and softwood have no relation to the actual hardness of the wood. Sapwood is the living wood on the outside of the stem. Heartwood is the inner core of physiologically inactive wood in the tree. Heartwood is usually darker than sapwood. 

Propiovanillone has been identified in Quercus rubra wood (152) and some phenylglycerol compounds are also found in various woody species. Thus, guaiacylglycerol (33) has been found in the sapwood of western hemlock (11) and the heartwood of Pinus resinosa (142). Further, the 1-O-glucoside and the 1-0-and 3-O-glucosides of p-hydroxyphenylglycerol have been reported from the inner bark of Larix leptolepis (105) and Picea glehnii (145), respectively, and an iso-prene derivative of the 3-(4-hydroxyphenyl)-propan-l-ol has been isolated from wood and bark of Zanthoxylum cuspidatum (86). 

In their work on the sterols of wood zones (sapwood to heartwood) H511 and Goller (37) found the inner heartwood of spruces contained about 3 pmoles of... 

While sapwood contains very little sterol in the ester form (traces to 0.15 moles/g, dry weight basis), the amount rises strongly to about 1.1 moles/g in the inner heartwood (37, 38). Holl and Pieczonka (38) found the acid component of the esters in both cases was comprised of a number of fatty acids. In terms of the usual nomenclature (chain length number of double bonds), the fatty acid composition of the steryl esters in spruce heartwood was found to be 12 0 (10%), 14 0(12%), 16 0(20%), 16 1 (12%), 18 0(14%), 18 1 (16%), 18 2(5%), and unidentified (11%). The composition varied only slightly from this in sapwood. In both sapwood and heartwood of the spruce, the ester was a minor form of the total sterol. The ester to free sterol ratio was about 1 2 in the inner heartwood (37). Sitosterol and other sterols have also been found to exist partly in the ester form in the heartwood of angiosperms - e.g., the slippery elm (Ulmus rubra) (24). Similarly, the sterols in the bark of the western white pine (Pinus monticola) are partly (60%) esterified (13). In both heartwood and bark the steryl composition of the ester fraction approximately reflected the composition of the free sterol fraction in that sitosterol was the major component followed by its 24-methyl analogs (13, 37). A similar situation has been observed with non-woody angiosperms - e.g., Zea mays (71). 

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