However, it is evident from anatomical and microchem- 
ical investigation that resistant fractions of cellulose oc- 
cur in many organic deposits of various geologic ages and 
that these resistant fractions are directly related to pre- 
determined structural features of the plant cell wall; 
hence they have their basis in the biochemistry of growth 
and differentiation of the cell wall. 
Since the ultimate loss of cellulose in plant remains 
may, under certain conditions, be delayed to varying 
degrees for immense periods of geologic time, it is appar- 
ent that simple generalizations can scarcely be made re- 
garding the complex processes of degradation in organic 
sediments as a whole. Chemical analyses of peat and 
humus have supplied data showing gross trends in the 
chemical alteration of plant remains in deposits (W aks- 
man, 1938). However, such empirical analyses do not 
correlate microchemical and anatomical aspects of degra- 
dation, and in general they interpret natural decompo- 
sition of plant remains in terms of plant substance rather 
than in terms of the complex organization of cells and 
tissues. It is significant, however, that the less favorable 
the conditions are for microbiological processes, the 
greater is the retention of the original cellulose in plant 
accumulations. With increasing geologic age, total loss 
of cellulose occurs through ‘‘coalification’’ and various 
changes associated with the transformation of plant resi- 
dues into higher rank coals. The problems of the earlier 
stages of cellulose degradation in anaerobic environments 
and of the processes of ‘‘humification’’ in general are 
in need of further co6rdinated anatomical, microbiologi- 
cal and chemical studies. Such investigations will be es- 
sential before a clear understanding of the major biologi- 
cal and chemical changes occurring between plant source 
materials and their geologic accumulation in the form of 
fossil fuels will be possible. 
[ 16 ] 
