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SUMMARY 
. Alteration of plant residues under anaerobic condi- 
ditions in organic sediments is a fundamental but 
inadequately known phase of the accumulation of 
carbon in nature. 
Details of anatomical changes during decomposition 
of plant tissues are of importance in the morpholo- 
gical interpretation of many structurally preserved 
plant fossils. 
. Anaerobic degradation of the plant cell wall involves 
certain basic structural changes which appear to be 
similar in all plant tissues; these changes are directly 
related to basic physical and chemical features in 
the organization of the cell wall. 
Degradation of the cell wall, either aerobically or 
anaerobically, is characterized primarily by loss of 
cellulose; the removal of cellulose most frequently 
follows a uniform sequence determined by the lamel- 
lar organization of the wall. 
The incidence of degradation of cell wall lamellae in 
lignified tissues occurs in the following sequence: 
1. Central layer of the secondary wall 
2. Innermost layer of the secondary wall 
Outermost layer of the secondary wall 
. Primary wall 
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The greater resistance of certain lamellae of the cell 
wall may be logically assigned to protection of the 
cellulosic framework by lignin and other ‘‘encrust- 
ing’’ substances. The persistence of unlignified pri- 
mary walls in fibrous peats, however, cannot be ex- 
plained by such mechanical protection, and demands 
an alternate explanation. 
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