416 DISEASES OF ECONOMIC PLANTS 



The rot, while chiefly of the heartwood, may, when 

 started, encroach upon the sapwood, even to the youngest 

 layers, and death may result by weakening the tree to the 

 breaking point. 



The causal fungus enters through wounds, particularly 

 broken stubs, and usually produces its sporophore at these 

 points after the rot has extended a meter or so in both 

 directions from the infection point. The first sure external 

 sign of the disease is the presence of the sporophores, al- 

 though sounding with the ax may sometimes be relied upon. 



The sporophores, numbering sometimes as many as 

 twelve on a tree, are shelving, hoof-shaped bodies from 

 25 to 30 cm. wide. The upper surface is brown, in later 

 stages black, hard, smooth, concentrically marked with 

 age, finally seamed and cracked. The pores are in layers, 

 approximately annual, and may bo 50 or even 80 in number. 

 The lower surface is gray to red-bfown. 



The trunk in cross section shows rot at the center; the 

 wood becomes soft and pulpy. The decayed region is ir- 

 regular in outline and bounded by narrow black layers. The 

 tree is rarely hollow, but remains filled wth the decayed 

 wood. Young trees which have no dead branches to admit 

 the fungus are usually immune. 



Infective material should be burned, wounds avoided, 

 and excision practiced in case of valuable trees. 

 V Red heart rot (Polyporus sulphureus (Bull.) Fr.). — 

 The conifers, also oak, cherry, chestnut, maple, walnut, 

 butternut, alder, locust, apple, pear, and many other trees 

 are affected. It is very widely distributed and destructive. 



The many-pored edible sporophores consist of a series 

 of overlapping shelves, two to twenty, or possibly more, 



