10 BULLETIN 1380, U. S. DEPARTMENT OF AGRICULTURE 
POCKET ROOT-ROT 
The small fructifications of Polyporus lignosus in a dry state 
closely resemble another common and widely distributed species 
which extends into the Temperate Zone and is known under a variety 
of names. This species is Polyporus zonalis Berk. (PL V, A), and it 
is found on the same set of hosts. It never attains the size of 
P. lignosus, and its texture is usually more firm, but its structure as 
regards the appearance of the hyphae in cross section is the same. 
Small dried specimens of both species are sometimes difficult to dis- 
tinguish. There are certain characters, however, by which they 
may be known. When fresh, P. zonalis is not so brilliantly colored. 
The upper surface is concentrically grooved and covered with a 
hard crust when dry. It is usually of a uniform wood or brown 
color, sometimes alternating with pale bluish or chestnut zones. 
There is not the contrast in color between the pore and context 
layers shown in P. lignosus. Although P. zonalis is sometimes pink 
or flesh colored it fades to a uniform gray or dingy white or wood 
color. The most reliable means of distinguishing between the two 
species in the field is in the character of the decays produced. 
The rot of P. zonalis is differentiated, showing well-defined pits 
or pockets, usually arranged parallel to the wood elements in 
the rot area (PI. V, A). In early stages of the decay these pockets 
may merely show in outline; later, however, the Wood in each indi- 
cated pocket disappears, leaving a cavity. The rot of P. lignosus, 
as has been indicated, is uniformly white or yellowish and undiffer- 
entiated. 
Polyporus lignosus is a parasite; i. e., it has the ability to attack 
living roots without the intervention of wounds or exposed dead 
wood. It continues to fructify, however, after the death of the 
host and may be found growing on all kinds of dead wood in the 
forest. It is a facultative parasite. Polyporus zonalis, on the 
other hand, is a wound fungus, depending upon a break in the bark 
or exposed dead wood to effect an invasion of its host. Under these 
conditions it has been found attacking the wood of wounds on 
living roots of Hevea and other jungle trees. Along a canal cut 
through the jungle near Para this fungus was found as a root rot 
on Hevea. The roots had been badly damaged by the workmen, 
with much dead wood exposed. The fungus had entered at these 
wounds and was causing a decay of the heartwood of the root. 
Near Riberalta in Bolivia the fungus was found causing a heart 
rot in the base of a young Inga species. A large open scar at the 
base of the tree with dead wood exposed was the means of entrance. 
Fruiting bodies appeared at this point. Thin sheets of mycelium 
with interlacing strands are also produced by P. zonalis. These 
sheets ramify over the substrata and through the surrounding 
forest litter. They are not conspicuous; the strands are delicate 
and seldom encountered. It is doubtful whether the fungus will 
be found of consequence on well-managed estates. 
The sporophores persist indefinitely in tropical countries, and all 
infested materials on the estate should be promptly burned. 
This fungus, under the name of Polyporus rugulosus, has been 
considered by Brooks the cause of a root disease of Hevea on the 
Malay Peninsula. 
