The ultimate fate of organic residues in nature is de- 
termined in large part by diverse factors of the environ- 
ment: physical, chemical and biological. The vast bulk 
of plant and animal remains is quite rapidly reduced, 
through complex energy-releasing processes, to simpler 
organic and inorganic compounds; and_ conversely, 
through complex energy-consuming processes these are 
re-incorporated into the tissues of living organisms. Con- 
spicuously active and effective in the biochemical decom- 
position changes are the fungi and bacteria. 
The rate of degradation due to microbiological activity 
is ordinarily most rapid in a warm, moist, highly aerobic 
environment. Favorable conditions are probably fulfilled 
to the greatest degree on or just below the surface of the 
soil. The ratio of accumulation versus degradation in the 
soil environment provides variable amounts of the so- 
called humus or organic component of the soil. If the 
environment is excessively wet, and more particularly 
if the availability of oxygen becomes deficient, the rate 
of degradation of plant tissues is greatly reduced. Such 
conditions reach their extreme in stagnant, poorly 
drained and relatively shallow basins such as swamps 
and bogs. Under such circumstances the accumulative 
phase exceeds the degradative phase and there results a 
gradual accretion of modified plant residues. In discuss- 
ing the degradation and preservation of plant tissues it 
is therefore essential that reasonable distinction be drawn 
between environments in which aerobic microbiological 
changes may proceed at a rapid rate, as in soil, and sub- 
aqueous environments of submergence and oxygen de- 
ficiency. This distinction seems to be of fundamental 
importance since the character of the degradative changes 
is greatly influenced, if not primarily determined, by the 
degree of these contrasting conditions of the biological 
and physical environment. It might almost be said that 
[2] 
