198 PLANT DISEASES 



various conifers, and also on some broad-leaved trees in 

 the United States. 



Poria laevigata, Fries, forms hard rusty-brown crusts 

 on the bark of birch trunks. A true parasite, destroying 

 the last-formed wood of each year, hence the annual rings 

 of wood become free from each other. 



Polyporus giganteus, Fr., often forms dense masses of 

 overlapping flaps or pilei, two to four feet across. The 

 pilei are thin, pliant, brownish, slightly zoned ; pores 

 minute, very short, becoming dark-coloured at once when 

 bruised, a character by which this species can be recog- 

 nised from allies. Often springs in dense masses from the 

 roots of living trees, and is probably parasitic. 



Fistulina hepatica. Fries. The beefsteak fungus ; re- 

 sembling overlapping flaps of liver in shape, colour, and 

 consistency ; grows on living oaks. 



Dedaelea quercina, Fries, is very common as a saprophyte 

 on oak stumps, and is also said to attack living oaks. It 

 is a bracket-shaped fungus, six to ten inches across ; 'the 

 entire substance is tough and corky ; pileus dingy white, 

 marked with concentric grooves. The hymenium consists 

 of thick, flexible plates, branching and anastomosing to 

 form long, wavy, irregular pits. 



DRY ROT 



(Merulius lacrymans^ Fr.) 



Although not destructive to living trees, ' dry rot ' is 

 so well known that a few observations culled from the 



