DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 527 



and frequently, become the prey of maggots which riddle them with 

 holes and burrows. It is also eagerly gathered by mycophagists who 

 know it to be an excellent article of food. 



The mycelium of the fungus may live in the dead wood of a tree 

 after it has been killed for a number of years, so that the same tree may 

 produce successive crops of edible fruit bodies. The destruction, which 

 the mycelium works, is characteristic. The heartwood is reduced to a 

 crumbly brown mass which resembles charcoal in its fracture, but is 



Fig. 189. — Fruiting body of Polyporus siilphureus. {After von Schrenk, Hermann, 

 Bull. 149, U. S. Bureau of Plant Industry, pi. iv, 1909.) 



red-brown in color. The decayed wood shows concentric and radial 

 cracks extending irregularly through it (Fig. 190). As the wood is at- 

 tacked and destroyed by the spreading mycelium, these cracks increase 

 and in them are found leathery compact sheets of mycelium, which can 

 be isolated by reducing the decayed wood to a fine powder by the blows 

 of a hammer. The wood decays uniformly and is converted into a 

 brittle brown substance, which can be rubbed to a fine powder between 

 the fingers. Von Schrenk found that the youngest trees in which the 

 red heart-rot occurred were about 50 years old. The removal of dis- 



