ROOT DISEASES AND INJURIES 



81 



gills or plates on the under surface of the fruiting-body (Fig. 8). 

 The tree-roots are infected in several ways. The spores may 

 cause infection through wounds at the base of the tree or in ex- 

 posed roots. The black strands running through the soil may 



also penetrate the 



bark of the roots. 

 In this manner the 

 fungus spreads 

 through the soil 

 from the roots of 

 one tree to another. 

 This mode of infec- 

 tion accounts for 

 the occurrence of 

 circular areas of dis- 

 eased trees. Since 

 the fungus also com- 

 monly occurs as a 

 saprophyte on dead 

 wood, the fruiting- 

 bodies are produced 

 in great abimdance 

 on prostrate trunks 

 and on old stumps 

 for several years 

 after the affected 

 tree is dead. 



Fig. 8. — Mature fruiting-body of ArmUlaria meUea, 

 showing gills on under surface. 



Control. 



Root diseases are difficult to control since the condition of the 

 roots cannot be readily ascertained. By destroying the toad- 

 stools and removing the diseased roots or parts of roots, the 

 individual tree may be saved. In the orchard or forest, dis- 

 eased trees or groups of trees may be surrounded by isolation 



