The molecules of wood cellulose are roughly a thousand 
times heavier than those of hemicellulose. They are linear and 
homopolymeric, composed of some 8,000 to 12,000 glucose 
units (beta-1,4-glucan). In vascular tissue, they are aggregated 
into linear bundles, called microfibrils, of some 40 molecules 
each. The microfibrils possess both crystalline and amorphous 
regions, depending upon the degree of order in the arrangement 
of the cellulose macromolecules within the microfibrils. The 
strength of the plant cell wall is due primarily to the construc- 
tion and conformation of these microfibrils. Cellulose further 
imparts the property of elasticity to wood. 
The hemicellulose polymers are branched noncellulosic 
polysaccharides which yield several hexose (mannose, galac- 
tose, and glucose) and pentose (xylose and arabinose) sugars 
upon hydrolysis, the amounts of each monomer being variable, 
depending upon the particular wood sample. Generally, the 
mannan content is greater in softwoods than in hardwoods. For 
xylan, the reverse Is true. 
Lignin is a complex polymer of variable structure and high 
molecular weight. It is composed of methoxylated phenyl- 
propane derivatives. Upon mild oxidative degradation, lignins 
yield substantial amounts of phenolic aldehydes. Vanillin is the 
dominant aldehyde formed from softwoods. Hardwoods yield 
both vanillin and syringaldehyde as major products. Because 
of the persistence of lignin in anoxic sedimentary settings, 
albeit in somewhat altered molecular form, phenolic aldehydes 
generated from organic-rich sediments may be potentially use- 
ful as geochemical indicators of the contributing source mate- 
rial (Leo and Barghoorn, 1970; Gardner and Menzel, 1974; 
Hedges, 1974). 
Unlike the polysaccharide polymers, lignin is hydrophobic. 
Furthermore, it is more resistant than holocellulose to decay. 
Hence, because of these properties and its intimate structural 
association with the polysaccharides in wood, it helps to pro- 
tect the latter from decay. In addition, lignin imparts rigidity to 
the cell wall. Without this property, the upward growth of trees 
would be severely limited. 
Additional detail on the chemistry of wood can be found in 
Browning (1963), Kirk (1973), Miller (1973), Northcote (1972), 
Sarkanen and Ludwig (1971), Stewart (1966), and Wise and 
Jahn (1952). For information on wood structure, see Alber- 
sheim (1975), Bailey (1954), Coté (1965), Harlow (1970), Isen- 
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