148 College of Forestry 
‘describing their appearance in a section of wood. In reality 
they are thin zones of discolored wood which at first sharply 
separate the various stages of decay in the wood. If, how- 
ever, the decay starts from several centers the dark zones 
extend very irregularly throughout the whole mass. Longi- 
tudinal sections of trunks in the early stages of decay show 
that these blackish zones extend for varying distances up and 
down the stem, their general course being parallel to the 
elements of growth. Their course, however, is In no way 
influenced by the annual rings of growth, but only by the 
progress of the decay effected -by the fungal hyphe; they 
may cross and recross the growth rings repeatedly. 
These blackish zones are not constant in position, since 
the decomposition products which cause the discoloration 
move forward with the advance of the decay in any part of 
the stem and ultimately disappear upon its completion within 
that part. The continual occurrence of the blackish zones 
between decayed and undecayed wood is due to the fact that 
the decomposition products are destroyed, together with the 
wood containing them, while new ones are formed constantly 
from the sound wood as fast as it 1s attacked by the advancing 
mycelium. 
The prominent blackish zones which are- such charac- 
teristic features so commonly associated with many of the 
decays of deciduous woods are of rare occurrence in decay- 
ing coniferous woods. Similar formations are characteristic 
of various decays of coniferous woods, but they are incon- 
spicuous when compared to the broad zones of decomposition 
products which commonly occur in the decay of dicotyled- 
onous woods. Such decomposition products arising through 
the decay of coniferous woods by wood-destroying fungi, 
although of common occurrence, apparently are small in 
quantity compared with those arising through the decay of 
dicotyledonous woods. Such being the case, this difference 
must be attributed to the inherently dissimilar character of 
these respective groups of woods. 
Macroscopic examination shows that these discolored zones 
are composed of wood of unusual hardness. Microscopic 
