83 



thickly set with small pores on the walls of which vast iiurnhers of 

 spores are prodiiced. The fniit bodies are perennial. Each year a new 

 pore bearing layer is added. A ciosei3'- allied species of f Uxigns ( Fotnes 

 Everhartii ) causes a heart rot of the yello'vt' birches, accompanied by ir- 

 regular, black jagged masses having the appearance of large warts. 

 These are probably abortive fruit bodies. Since the white heart rot is a 

 wound fungus, one means of control is the prevention of wounds. This is 

 not aKvays possible especially in large forest areas. The best method of 

 combating the disease is the removal of the sources of infection, the dis- 

 eased trees. Removing the fruiting bodies may be of some value but many 

 of them may be overlooked or be inaccessible, and in any case they -will 

 soon be renewed. 



Abortive Fruiting Bodyeof the.White HeartjRot. Fomes igniarius. (After Von Schrenk) 



( c ) Red Heart Rot. This disease of deciduous trees is caused 

 by one of the pore fimgi ( Polyporus sulphureus ) .The heart wood of infect- 

 ed trees becomes a mass of reddish brown wood which is characterized 

 by radial and concentric cracks. These cracks become filled with thin 

 sheets consisting of interwoven threads of the fungus. This fungus does 

 not seem to be very common in Canada. 



