258 Minnesota Plant Diseases. 



The parchment pore-fungus rot (Polystictus pcrgamcnus Fr.\ 

 This is an exceedingly abundant pore fungus found on various 

 kinds of soft wood trees. It is very common on birch, where 

 one frequently finds whole logs covered w r ith the densely 

 crowded fungus shelves. Occasionally one finds the fungus on 

 the living trees. It has also been observed on living larch trees 

 where it occurs in great abundance. The fruiting body is a 

 thin, reflexed shelf which is very light tan colored above and 

 covered with dense hairs. The pores are found on the lower 

 surface and are shallow at the edge, increasing in depth toward 

 the center. They are often of a purplish or violet tinge and 

 the pore walls become, with age, so badly torn that the under 

 surface of the shelf has the appearance of a toothed or hedge- 

 hog fungus. There is strong evidence that it has caused the 

 death of numerous larch trees in Minnesota. (Fig. 36.) 



Wood-rot of the creeping pore-fungus [Polyporus vapor a- 

 rius (P.) Fr.~]. This fungus is reported as very abundant in Eu- 

 rope and forms very similar to it are known in Minnesota. A 

 description of this fungus will therefore not be out of place 

 since it is not improbable that it exists in the state. The fun- 

 gus attacks chiefly soft coniferous woods and is a wound para- 

 site. It is found in the roots and on the stem and is a danger- 

 ous enemy to trees. The mycelium develops in cracks and un- 

 der the bark, forming a dense, white felt and causing rapid de- 

 cay of the wood. The fruiting bodies are white, flat, prostrate 

 forms and do not produce shelves. The pores are small and cover 

 the upper surface of the fruiting body and are very numerous. 

 The mycelial felts and strands are not unlike those of dry rot 

 and the disease is often confused with that of true dry rot. It 

 is frequently found in the timbers of dwellings where it is a 

 dangerous agent of decay very similar in its action to that of 

 the dry rot fungus. 



The zoned Polyporus rot [Polystictus versicolor (L.) Fr.]. 

 This is one of our commonest of pore fungi, found chiefly on 

 old stumps and decayed timbers. The shelves are thin and 

 leathery and conspicuously zoned above. The zones are of dif- 

 ferent colors varying from light tans to very dark brown or 

 black and are frequently velvety in appearance. The pores are 

 on the under surface and are very small. They are white at the 



