7. It is proposed, although it cannot be demonstrated 
within the scope of this study, that the greater re- 
sistance to hydrolysis of the primary wall and the 
outer secondary wall layeris due to chemical differ- 
ences in the organization of the cellulosic matrix, 
rather than solely to a physical relation with lignin 
and other protective complexes. 
8. The ultimate loss of cellulose in organic deposits 
may be delayed for periods measured in terms of 
geologic time, as shown by its presence in lignites 
of Tertiary and older age. The rate of loss, however, 
is greatly influenced by the initial biological condi- 
tions of deposition as well as by subsequent environ- 
mental changes accompanying ‘‘coalification. ”’ 
9. Mineralization of plant remains apparently often oc- 
curs at a stage when cellulosic structural residues are 
still retained. Infiltration and precipitation of min- 
erals, such as silica and calcium carbonate, occasion- 
ally cause a ‘‘fixation’’ of structure which, in min- 
eral form, retains a large measure of biological detail. 
Such petrifactions may or may not retain a rather 
high percentage of the original, though chemically 
modified, organic matter during subsequent geologic 
change. 
9 
10. Many aspects of the problem of ‘‘humification’”’ and 
‘*eoalification’’ of plant residues are known only in 
empirical terms. An adequate understanding of 
these complex processes will necessitate extensive 
coordinated microbiological, anatomical and chemi- 
cal investigation. 
Institute for Research in General Plant Morphology 
Harvard University 
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