100 College of Forestry 
the secondary layers and remains in place long after the 
disappearance of the secondary and tertiary lamelle of the 
cell-wall. After the secondary layers of thickening have been 
dissolved, the resulting woody tissue has a skeletonized ap- 
pearance (Plates X XII and XXIV, Fig. 1). It has all of. 
the elements but their walls consist principally of the middle 
lamelle. ‘These retain the nature of lignified walls and offer 
considerable resistance to dissolution, and are the last portion 
of the individual cell-wall to disappear. However, they too 
gradually become thinner and thinner until they break up 
into irregular fragments. It is not until they have disin- 
tegrated to this extent that the middle lamellze respond to 
the cellulose test with chlorzinc-iodine. The corners of the 
middle lamelle, where they are thickest, are the last to 
disappear. 
Within the decayed areas the uniseriate pith-rays fre- 
quently are dissolved out quickly early in the course of the 
decay. ‘These are the first elements to disappear and doubt- 
lessly disappear first because of their exceedingly thin cell- 
walls, as explained earlier. I*requently the medullary rays 
are dissolved entirely while cell-walls of normal thickness 
may be found immediately adjoming them on both sides 
(Plate XXII). The thick vessel walls are strongly lignified 
and are the last elements to disappear. They continue to 
respond to tests for lignification long after the surrounding 
cell-walls fail to do so and frequently persist quite intact 
while the surrounding cell-walls are dissolved until only the 
middle lamellze remain. In still later stages of decay, the 
partially disintegrated vessel walls often are the only ele- 
ments remaining within the pockets. They are retained in 
their original positions within the pockets by reason of being 
held in place by numerous mycelial threads which penetrate 
their walls in all directions. Where two or more vessels are 
contiguous, they frequently separate before they are entirely 
dissolved. Where they remain attached until completely 
decayed, however, the common walls between two or more 
vessels are the last portions to be decomposed by the action 
of the fungus. Finally even the resistant vessel walls become 
