212 The Philippine Journal of Science wis 



quently a gray to dark brown discoloration appears in the vicinity 

 of the bast. The chief internal symptom is the stoppage of 

 latex flow, due to some abnormal condition of the latex tubes. 



Causal organism. — No causal organism has been associated 

 with the disease. It appears to be due to some abnormal physio- 

 logical condition, which may be inherent in certain trees; how- 

 ever, in certain cases trees appear to recover. 



Control. — Tapping should be discontinued for a period of years 

 on infected trees. Seeds for propagation should never be selected 

 from diseased trees. 



ROOT DISEASE: FOMES LIGNOSUS (KL.) BRESADOLA 



Symptoms. — The disease is most severe upon young trees from 

 1 to 3 years old. Frequently diseased patches are produced 

 in plantations. Diseased trees at first show a yellowing of the 

 leaves, which is followed by a wilting and death. Dead trees 

 can be easily pulled up or pushed over. The diseased roots 

 are characteristically covered with a white mycelium, which 

 may be in the form of strands spreading over the root or in 

 the form of a sheet covering the entire surface. The white 

 strands of mycelium spreading over the roots are the charac- 

 teristic symptoms. These strands may be 0.5 to 1 centimeter 

 broad and may be divided into finer strands that spread to the 

 lower portion of the trunk and to the extremities of the roots. 

 The diseased roots and lower trunk are not discolored, but 

 become soft, like punk. The fungus also develops well on a 

 number of jungle trees and stumps where it produces the same 

 symptoms. 



Causal organism. — The mycelium growing over the surface 

 of the roots penetrates into the tissues, thereby causing death. 

 The cortex and wood are completely invaded by the mycelium. 

 From diseased roots the mycelium can spread through the ground 

 to the roots of healthy trees. This is one of the chief methods 

 of spread and accounts for the disease appearing in patches 

 throughout the plantation. Fruiting bodies of the fungus are 

 not usually produced on rubber trees, because the diseased trees 

 are usually burned as soon as found. If diseased stumps are 

 left standing, the characteristic fruiting bodies will be produced. 

 They are more commonly found on stumps of jungle trees and 

 are always produced above ground. 



The fruiting bodies are at first orange yellow cushions, which 

 later develop into flat, somewhat semicircular plates. They are 

 usually 8 centimeters long, 4 centimeters wide, and 1 centimeter 

 thick behind, but may attain a width of 30 centimeters. They are 

 perennial and woody, belonging to the "bracket fungi." At first 



