polysilicic acid is known to occur in nature, forming from the 
very rapid weathering of certain aluminosilicates with a high 
silicon to aluminum ratio, such as plagioclase and some of the 
mafic minerals (R. Siever, personal communication). When 
released into natural waters, it is likely to depolymerize to 
monosilicic acid. But if wood is encountered before de- 
polymerization can take place, there is the possibility it might 
be absorbed into the wood through hydrogen bond interaction 
with the hydroxylated wood constitutents. Thereafter, through 
further polymerization as before, the silica can build up as a gel 
of gradually increasing density. Hence a petrifaction results. It 
would be most interesting to learn if the specific types of 
volcanic ash, which have served as sources of wood silicifica- 
tion in the past, do truly release polysilicic acids when they are 
fresh and first exposed to the elements of weathering. 
It is not clear whether or not a certain amount of degradation 
is essential for attaining a high degree of petrifaction under 
sedimentary conditions. Decay would significantly increase 
permeability of cell walls, create greater void space in which 
more silica could be deposited, and perhaps more importantly, 
increase the number of active sites for potential bonding in- 
teraction. The removal of one or more of the wood constituents 
— hemicellulose, cellulose, or lignin, would leave free sites 
available for bonding on the molecules remaining. Also, the 
degradation products from both the lignins and the polysac- 
charides, e.g., phenolic aldehydes resulting from mild oxida- 
tive degradation (either microbial or chemical) of lignin or 
pentose or hexose monomers from polysaccharide hydrolysis, 
would result in chemical entities with more active sites per unit 
volume than their parent materials. Such degradation products 
might not immediately migrate from the cell wall region from 
which they were derived and might possibly be immobilized 
within the cell wall by reaction with silicic acid. Unless decay 
has progressed to an advanced stage, this situation would not 
be detectable by light microscopy alone. 
Consideration of the nature of water in wood lends further 
plausibility to the suggestion of bonding involvement in pet- 
rifaction. The hysteresis® effect in wood is attributed to the 
presence of hydrogen bonds among the polysaccharides in 
‘Hysteresis is the term applied to the variance in the sigmoid moisture content — 
relative vapor pressure curves, depending on whether equilibrium is approached from 
a higher or a lower relative vapor pressure (Wise, 1944). 
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