EXPLANATION OF THE ILLUSTRATIONS 
Piare I. Fia. 1. Transverse section of the wood of a sub- 
merged white pine stump, age about 2000 years, showing 
differential degradation of the cell wall. Note the presence 
of some intact cell walls, others incipiently degraded and 
many cells in which the secondary wall is largely reduced to 
a lignin residue occupying the center of the lumen, 70. 
Fic. 2. Transverse section of the same material showing 
incipient degradation of the secondary wall of an isolated 
tracheid (center) surrounded by cells in which the secondary 
wall has been largely degraded. 170. 
Fic. 38. Transverse section of the same, but more highly 
magnified. Note the discrete mass of the ‘‘coagulated’’ rem- 
nants of the major part of the secondary wall in the center 
of each cell. 870. 
Fic. 4. Tangential longitudinal section of the same material. 
The dark, heavily stained amorphous material represents the 
degraded remains of the central and inner layers of the sec- 
ondary walls. 100, 
Fic. 5. Transverse section of a spruce pile, submerged in 
marine silt for 100 years. This section from the outer rings 
of the pile shows incipient degradation of the central and 
inner layers of the secondary wall. 500. 
Fic. 6. Transverse section from a different part of the white 
pine stump shown in Fig. 1. Note the complete breakdown 
of the central and inner layers of the secondary wall and the 
retention of the primary wall and the outermost layers of the 
secondary wall. 500. 
