in general, of the entire plant body. The cell wall is com- 
posed initially, in its development from pre-existing cells, 
of a primary wall, This primary wall is a cellulosic layer 
(or series of layers) which ordinarily increases in surface 
area and may vary in thickness during the growth and 
enlargement of the cell. After growth and enlargement 
have ceased, a secondary wall may be formed, always in- 
ternal to the primary wall. In many plant tissues, partic- 
ularly in reproductive organs, secondary walls are not 
formed, and, in such cases the primary wall may become 
thick and conspicuous, comprising the bulk of the cell 
wall. In the cell walls of wood and woody plant tissues, 
however, thick secondary walls are ordinarily developed, 
the major topographic and structural feature of such tis- 
sues being their greatly thickened secondary walls. 
The secondary walls of cells in woody tissues consist, 
except in certain cases, of three morphologically distinct 
layers or lamellae (Bailey and Kerr, 1985; Bailey, 1988; 
1940). The innermost and outermost of these lamellae 
comprise relatively thin aggregations of cellulosic wall 
substance in which the crystalline cellulose aggregates 
tend to be oriented more or less transversely, or in helices 
of low pitch. The central and ordinarily thickest layer 
of the secondary wall, on the other hand, is composed 
most commonly of crystalline cellulose which tends to be 
oriented more nearly vertically, or in helices of steep pitch 
(Bailey, 1940). All three cellulosic lamellae may be in- 
filtrated to varying degrees with encrusting substances 
such as lignin, terpenes, resins or other ‘‘protective”’ 
chemical complexes which retard biological and chemical 
degradation. 
In the anaerobic degradation of wood it has uniformly 
been found that a consistent sequence of degradative 
changes occurs. This sequence shows a significant and 
fundamental relation to the lamellar structure of the cell 
[ 6 ] 
