Minnesota Plant Diseases. 259 



surface when fresh. The pore walls often become torn with 

 age. The shelves vary somewhat in size; they are generally 

 from two to three inches across and are aggregated together 

 into very dense clusters in shingle fashion. They appear usual- 

 ly when the logs or branches upon which they form are in ad- 

 vanced stages of decay. The zoned pore fungus is perhaps not 

 of great importance as a timber rot, though it is very frequent 

 on railroad ties. 



The pitch-stemmed pore-fungus rot (Polyporus picipes Fr.\ 

 This form of pore fungus is conspicuous in our woods on account 

 of its large, thin fruiting todies which are attached by a short 

 black stem. It occurs on broad-leaved trees and is usually found 

 on decaying logs or stumps. It has been reported as occurring on 

 living trees but little is known of its relationship with the latter. 

 Though not uncommon, especially in hard maple and basswood 

 forests, it is not usually very abundant. The fruiting bodies 

 are thin and tough, leathery when moist, becoming brittle when 

 dry. They are usually broad-beaker-shaped to flattened when 

 mature, are dark red-brown above and have a short central 

 'black stem. The fruiting bodies are not at all fleshy. The 

 lower surface, which contains the very minute pores, is dirty 

 yellow in color. 



The hairy pore-fungus rot (/ 'olystictus hirsntus />.). This is 

 a very common shelf-pore form which occurs abundantly on 

 dead sticks and limbs of trees. It has been reported also on 

 living trees of hornbeam, alder, birch and oak but exact details 

 of its relationships with these plants are wanting. 



