82 



Another common root rot of coniferous trees is due to a pore fungus,, 

 Polyporus Schweinitzii. The place of attack is the root, from which it 

 passes to the trunk. The decayed wood becomes brittle and \ellow. The 

 fruiting bodies are large, dark brown, and som.ewhat spongy in texture. 

 They may be sessile or stalked. The spore bearing surface is brownish 

 ■with a rose tint when young. It rapidly turns diark when bruised. In Eu- 

 rope it is usual to prevent the spread of the disease by trenching. Infect- 

 ed trees should be destroyed. 



Polyporus betulinus. 



Heart Rots. Among the most serious diseases of trees are the heart 

 rots, usually caused by some species of the pore fungi. The mycelium en- 

 ters by a wound and grows into the heart wood, penetrating through 

 or among the cells. It produces substances that break down the cells, 

 and the wood disintegrates. The fungus spreads until the tree is ruined 

 for timber. Usually the fruit bodies of the fungus do not appear until the 

 decay is far advanced'. 



( b ) The White Heart Ret ( Fomes igniarius ) . The most ser- 

 ious of the heart rots in this region is that caused by the pore-fungus 

 ( Fomes igniarius ) . It attacks all broad-leaved trees but in Eastern Can- 

 ada the beech suffers most, w^hile in the west it is most common on the 

 poplar. 



The centre of the attacked tree becomes reduced to a w^hitish pulpv 

 mass of decayed wood bounded on the outside by one or more narrow, 

 irregular black bands. The fruit bodies are produced on the trunk. 

 They are hoof-shaped and in old ?pi cimens the upper surface is black in 

 color and much rouorhened and cracked. The lo\ver surface is bro\vn and 



