80 



MANUAL OF TREE DISEASES 



roots (Fig. 6). The strands may be traced to points at which 

 they enter the roots. At these points the white mycelium in- 

 side the black strands spreads out and runs in all directions in 

 the bark and sapwood. Thin white sheets of mycelium are 

 found in the cambiiun region (Fig. 6). The tissues of the 

 cambium and bark are destroyed and replaced by the white 

 sheets. The mycelium also penetrates the medullary-rays and 

 sapwood and causes a wet white rot. After the bark is killed, 

 the black shoe-strings are formed abimdantly between the 

 bark and wood. They anastomose in all directions and form 



a network. The decayed 

 area of sapwood and bark 

 is bordered by a brown 

 zone. 



The fruiting-bodies of the 

 fungus are honey-colored 

 toadstools or mushrooms. 

 They appear on the sides of 

 the trunk, exposed roots or 

 directly from the groimd. 

 Close examination will show 

 their attachment to the 

 black shoe-strings (Fig. 7). 

 The toadstools occur in 

 clusters, attached to one another at the base of the stalks. 

 The stalks are somewhat swollen at the base and have a fragile 

 collar just beneath the cap. The upper surface of the cap 

 is smooth and yellowish or brownish. The imder surface is 

 composed of radiating pendent plates or gills of the same 

 color (Fig. 8). 



Catise. 



The shoe-string root-rot of trees is caused by the mushroom, 

 Armillaria meUea. The spores are borne on the sides of the 



Fig. 7. — Young toadstools of ArmiUaria 

 meUea attached to shoe-strings. 



