106 College of Forestry 
structure is noteworthy when one considers that these differ- 
ences are brought about solely by minor structural differences 
of certain elements of these respective woods, in this case the 
elements being the medullary rays. 
The inner fibrous bark of the sugar maple decays quite 
rapidly and soon becomes soft and spongy. The outer scaly 
bark, however, owing to its corky nature, is quite resistant 
to decay. 
Microscopic Characters of Decayed Wood.— The dissolu- 
tion and course of the delignification of the woody elements 
is essentially the same as that described for yellow birch. In 
fact it differs from the decay of yellow birch only in so far 
as would be necessitated by the different structure of sugar 
maple wood. 
The solvent action of the fungus proceeds very irregu- 
larly. Often cells, whose entire walls still respond strongly 
to lignin tests, are left among cells which have been decom- 
posed to such an extent that only the middle lamellee remain. 
The wood prosenchyma and w ood parenchyma elements are 
the first elements to disappear. In this connection it will be 
remembered that these elements were less strongly lignified 
than any of the other elements of the growth ring. In see- 
tions of badly decayed wood, the effect of the numerous lar ge 
pith-rays in retarding the decay from spreading tangenti- 
ally is ‘strongly exemplified. In addition, the terminal ealls 
of the growth rings, which are very resistant to decay, are 
potent factors 3 in retarding the spread of the decay in a radial 
direction. Their retarding effect, however, is less than that 
offered by the medullary rays. As a result of the structure 
of the wood and the method of decay induced by this fungus, 
the decay necessarily would proceed most rapidly up and 
down the stem, less rapidly in a radial direction, and least 
rapidly in a tangential direction. Within each growth ring 
the wood elements which adjoin the vessels decay less rapidly 
than the more distant-lying ones, excepting the ‘few lavers of 
tangentially flattened ells on the outer face of the erowth 
ring. In sections of wood in an advanced stage of “decay, 
aside from this resistant zone of wood, the vessels with a 
