4° 



Minnesota Plant Diseases. 



Wood-dwelling habit. A great host of saprophytic fungi 

 grow upon wood — on sawed timber, fallen logs and on the ex- 

 posed heart wood of living trees. They constitute the great 

 timber diseases — the chief agents of the rot of wood. Railroad 

 ties, mine timbers, house foundation timbers, in fact, wood, 

 wherever it is placed in continuously moist, dark places, quickly 

 undergoes a rotting which is caused by these fungi. The wood 

 of all our trees is subject to the attack of some of these fungi, 

 but one kind of fungus is often confined to one kind of tree 

 timber. For instance, the birch pore fungus is found only on 

 birches. As a general rule, these fungi are not able to live in 

 the bark of trees, hence they can gain entrance to the wood of 

 living trees only through wounds in the bark. When once such 

 an entrance has been obtained, the fungus remains in the heart- 

 wood — which is of course dead even in healthy trees — and sets 

 up a decay which may finally cause the tree to become hollow. 

 Such a hollow tree may live for years, since the attacking fungi 

 may be unable to injure the sap wood in which the living 



cells are found. Wood-inhabit- 

 ing fungi obtain their nourish- 

 ment from the wood in which 

 the mycelium is buried. The 

 "woody" character of wood is 

 largely given to it by a substance 

 known as lignin. The timber 

 saprophyte is able to secrete a 

 chemical which can break down 

 this lignin just as the ferment of 

 the yeast cell breaks down sugar. 

 When the lignin is broken down 

 the wood no longer gives the 

 characteristic chemical tests for 

 lignin. The wood has then been 

 converted into "punk," is brittle 

 and soft and crumbles readilv. 

 This action of the fungus is in 

 all probability often aided by the 

 action of bacteria. Wound sap- 

 rophytes gain entrance to the 



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Fig. 19. — A wood-dvvellmg fungus (Dal- 

 dinia vernicosa) on a dead stick of 

 wood. This is a burnt-wood fungus. 

 Original. 



