Dec. 1, 1924 
Diagnosis of Decay in Wood 
527 
THE CLASSIFICATION OF WOOD 
HOTS 
Very often decays are placed in two 
main divisions, heart rots and sap rots, 
on the basis of the parts of the wood 
attacked. The sap rots may be again 
divided into the decays of the live 
sapwood, such as those produced by 
Polyporus dryadeus or Fomes igniarius , 
and the decays of the dead sapwood 
and also heartwood, such as that pro¬ 
duced by Polystictus abietinus Dicks, in 
conifers. 
Frequently the heart rots are classi¬ 
fied with respect to the longitudinal 
portion of the tree attacked. The 
decays found in the main portion of 
the tree are termed trunk rots (fig. 1, A); 
those found in the upper trunk, top 
rots; those found in the lower, basal 
portion, butt rots. The butt rots 
usually extend some distance into 
the heartwood of the roots (fig. 1, A). 
The decay produced by Polyporus 
schweinitzii Fr. is of this type. The 
term root rot is usually applied to a 
sap rot of live roots of which the 
Armillaria mellea (Vahl.) Quel, decay 
is a good example. 
A classification based upon the par¬ 
ticular reaction produced in the wood 
by the fungus seems of greater value in 
decay diagnosis. There are two groups 
due principally to the particular chem¬ 
ical or enzymic reaction of the fungus 
with the wood, which show the color 
distinction mentioned above (p. 526). 
The white rots are caused mainly by 
the lignin-dissolving fungi, although 
they, are not restricted to this type. 
They are usually whitish in the areas 
where the decay has reached the 
typical stage. These areas are prin¬ 
cipally composed of white cellulose 
compounds or are bleached to a 
whitish color as a result of the fungous 
action. The white rots may be divided 
into white pocket rots, white ring 
rots, white mottled rots, and white 
spongy rots (PI. 1, A, B, C). The 
second group, comprising the brown 
rots, caused mainly by cellulose-dis¬ 
solving fungi (but not limited to 
these), shows yellowish, reddish, or 
brownish discolorations in the typical 
stage. Usually the cellulose has been 
extracted for food by the fungus, leaving 
the lignin compounds in the remaining 
wood tissues. Under the brown rots 
of the coniferous woods the subgroups 
are brown pocket rots, brown ring rots 
and stringy rots, brown cubical rots, 
brown spongy rots, and brown mottled 
rots (PI. 2, A, B, C). 
Of the fungi treated in this study, 
Trametes pini (Brot.) Fr. (Fomes pirii) 
(Brot.) Lloyd and Polyporus anceps 
Pk., represent the white pocket rots. 
Fomes igniarius Linn, represents the 
white spongy rots; Echinodontium tinc- 
torium E. and E. represents the brown 
ring rots and stringy rots; Pholiota 
adiposa Fr. represent the brown 
mottled rots; Polyporus amarus Hedg. 
represents the brown pocket rots; and 
Polyporus schweinitzii Fr., Polyporus 
balsameus Pk., Lenzites sepiaria Fr, 
Trametes carnea Nees. and Lentinus 
lepideus Fr. represent the brown 
cubical rots. The principal groups of 
wood rots are thus represented. More 
brown cubical rots than other types are 
discussed because this group appears to 
contain rots the incipient stages of 
which are often not distinguishable by 
discolorations of any kind, $nd which 
for this reason present a serious problem 
from the economic viewpoint. 
Certain fungi produce in wood cells 
changes slightly resembling those foufid 
in true decay (88). These are the 
wood-staining or sap-stain fungi, of 
which the blue stain fungi, Cera- 
tostomella spp., are representative (34). 
Their hyphae have been observed pene¬ 
trating the tracheid walls in the woods 
of pine and other species (36, 37, 57, 
72 ). Penetration is not frequent, how¬ 
ever, and is not so prominent a decom¬ 
position process as that produced in the 
medullary rays where the walls of the 
ray cells are often completely broken 
down. More commonly the hyphae in 
passing from cell to cell seek the 
natural openings, the bordered pits,, 
where the netlike perforated mem-, 
brane supporting the torus apparently 
presents an easy passageway, or they, 
pass through the simple pits in the cell 
walls. 
GROSS CHARACTERS OF DECAY 
CpLOR.— The discolorations usually 
associated with the stages of a particu¬ 
lar decay are the most valuable 
diagnostic characters visible to the 
naked eye (Pis. 1 and 2). They vary 
greatly for different fungi and slight 
variations may be noted for the same 
fungus in different hosts. Color forms 
the basic part of rot descriptions, but 
these descriptions,’ of course, can not be 
presented in detail here. However, 
the discolorations produced in wood by 
the advancing hyphae of wood-rotting 
fungi should be given more than 
passing attention because it is the 
incipient stage that in many cases 
eludes detection. 
Only a few important rots have strik¬ 
ing or even visible incipient discolora¬ 
tions. These are more common in 
