528 
Journal of Agricultural Research 
Vol. XXIX, No. 11 
white rots, but quite absent in brown 
rots, particularly brown cubical rots 
and brown pocket rots. 
The incipient discoloration produced 
in wood by Trametes pini (PI. 3, A) 
exemplifies the invasion discoloration 
found in many white pocket rots. It 
is so common in the lumber and timber 
of commerce that it is known as “red 
heart” or “firm red heart.” It occurs 
in nearly all species of coniferous wood 
and is almost entirely confined to the 
heartwood. According to the host and 
the conditions of development of the 
fungus, the “red heart” varies from 
pinkish to dark reddish or browmish or 
sometimes a purplish color. While the 
appearance of a distinct color in the 
wood may indicate the presence of de¬ 
cay, identification is complicated by 
the fact that such fungi as Polyporus 
anceps Pk. and Fomes annosus Fr., 
which produce white pocket rots, also 
cause pinkish to reddish discolorations 
in the incipient stage of rot. Polyporus 
circinatus has recently been collected 
in Minnesota on roots of living Picea 
mariana, producing in this wood a 
white pocket rot having a light to dark 
reddish incipient discoloration. This 
observation, verified by cultures, adds 
another to the list of fungi producing 
reddish discoloration in heartwood. 
The incipient stages of certain brown 
rots, such as produced by Fomes laricis , 
Polyporus sulphureus, Polyporus schwei- 
nitzii, Fomes pinicola, and others, in 
certain hosts may often be confused 
with each other or with the invasion 
discolorations produced by the white 
pocket-rot fungi. The natural pinkish 
or reddish color of the heartwood of 
certain hosts, such as Pseudotsuga taxi- 
folia, adds to the confusion. Certain 
invasion discolorations take on the na¬ 
ture of a water-soak in the infected 
wood of freshly cut trees. This is 
characteristic of the incipient stages of 
the white rots produced by such fungi 
as Ganoderma tsugae in Tsuga canaden¬ 
sis (PI. 3, B), and Polyporus dryophilus 
in broadleaf hosts. According to Long 
(46, 48), Polyporus pilotae and Stereum 
subpileatum also produce a water-soak 
in the incipient stage of decay. In the 
case of Ganoderma tsugae the water- 
soaked areas soon lose their definition 
on drying, and little or no discoloration 
remains to indicate the incipient decay 
areas. 
In the incipient stage of decay pro¬ 
duced by Echinodontium tinctorium the 
incipient discolorations extend some 
distance ahead of the typical stage (fig. 
1 and fig. 2, B). Where the discolora¬ 
tions fade out and for some distance 
beyond this limit, the action of the 
fungus on the wood structure contin¬ 
ues. Consequently, sound-appearing 
boards cut from infected areas in the 
logs show a brashy, crumbly texture 
which unfits the stock for commercial 
use when seasoned ( 9 , 64 , 85). Poly¬ 
porus anceps , probably identical with 
Polyporus ellisianus as used by Long 
(49), produces in Pinus ponderosa a 
characteristic incipient discoloration 
(fig. 2, A), which so far has not been 
observed in other hosts of the fungus. 
Reddish to reddish-brown areas radiate 
from typical rot areas viewed in trans¬ 
verse section. Lighter reddish dis¬ 
colorations have been noted in Picea 
canadensis infected with Polyporus an¬ 
ceps. White (89) states that when 
Fomes applanatus develops in living 
hosts the incipient decay is bordered 
by a brownish invasion zone one-fourth 
inch wide or wider. 
White considers this character is of 
diagnostic value. Fomes igniarius pro¬ 
duces in the incipient area a charac¬ 
teristic invasion zone, usually a dark 
band or zone of irregular outline and 
width (fig. 2, C). Pholiota adiposa 
produces in Tilia americana a dark 
brown, characteristic invasion zone 
which is often included within the area 
of typical decay as the invasion pro¬ 
gresses (fig. 2, D). Pronounced in¬ 
cipient discolorations are not observed 
frequently in the brown rots. The 
rot caused by Fomes pinicola in Tsuga 
heterophylla is an example, showing but 
a faint discolored area of incipient 
decay which does not form a con¬ 
tinuous band around the typical rot 
areas (fig. 2, E). Some incipient and 
typical discolorations common to com¬ 
mercial woods are well illustrated in 
the work of Boyce (9 ). 
The difference between white and 
brown rots in the typical stage is 
usually very clear. White rots com¬ 
monly show distinctive incipient dis¬ 
colorations and brown rots do not. 
Hence brown rots probably cause 
greater economic loss. The difficult}’ 
in diagnosis often lies in distinguishing 
decays in which the incipient discol- 
EXPLANATORY LEGEND FOR PLATE 1 
Three typical white rots (about natural size). A—White pocket rot caused by Fomes nigrolimitatus 
(F . putearius Weir) in Larix occidental™. Tangential section. B.—White pocket rot caused by Fomes 
extensus in a hardwood root (tangential section). C.—White mottled rot caused by Fomes applanatus 
in Populus grandidentata. Radial section. Dark-colored zone lines often accompany this rot. 
