hydrochloric acid. It is probable, therefore, that signi- 
ficant chemical as well as physical differences exist be- 
tween the first formed and the subsequently formed 
lamellae of the secondary wall. In these respects the 
outermost layer of the secondary wall more closely re- 
sembles the primary wall than it does the later formed 
lamellae of the secondary wall. 
The existence of a pronounced difference in the rate 
of degradation of the various cellulosic layers of a single 
cell wall presents a seeming paradox in the interpretation 
of cellulose decomposition. wo questions immediately 
arise: (1) what are the factors, biological or chemical, 
which cause the decomposition; and (2) what substance 
or substances impart such differential resistance to de- 
gradation within the cell wall itself? The fact that dif- 
ferential degradation of wall layers is not an isolated 
phenomenon, but instead a fundamental feature in the 
anaerobic decomposition of plant tissues emphasizes the 
significance of these questions and their bearing on the 
problem of cellulose decomposition in general. 
In a previous study by the author these questions 
have been discussed in some detail, particularly with 
reference to environmental conditions and the possible 
causes of degradation (Barghoorn, 1949). It has been 
proposed, though not proven, that the degradation of 
wood deeply submerged in marine sediments is probably 
due in large part to the hydrolytic breakdown of cellu- 
lose rather than directly to microbiological attack.’ It is 
probable, although again not proven, that the relatively 
high concentration of hydrogen sulfide (and associated 
hydro-sulfuric acid) in many carbonaceous marine sedi- 
ments is responsible in part for the gradual chemical 
'This conclusion does not question the apparently well established 
evidence confirming the existence of anaerobic bacteria at considera- 
ble depths in peat deposits (Thiessen and Strickler, 1934; Waksman, 
1930). 
Lo] 
