26 IOWA ACADBMT OF SCIENCE 



bracket or hoof shaped, hard and woody pileus, with concentric ridges, 

 azonal and stratified tubes. 



This genus includes some of the most troublesome of the wood para- 

 sitic diseases. The Fomes fomentarius on the beech, birch, and yellow 

 birch ; the F. pinicola on pines, spruces, balsam fir are excellent illustra- 

 tions of very destructive wood fungi. The F. applanatus, the largest 

 of our bracket fungi and one of the most common in Iowa, occurs on 

 the oak, maple, apple, plum, and many other deciduous trees. It is a 

 wound parasite though not as injurious as some of the others. 



Hartig" long ago worked out the pathological change that occurs in 

 the wood when attacked by H. igniarius. The germinating spores of this 

 fungus enter the plant through a wound, which may have been formed 

 by the breaking off of a branch during a wind storm or from a badly 

 pruned branch. The mycelium spreads into the wood and soon reaches 

 the heart wood which it changes into a brown color, then into a whitish 

 friable substance. The mycelium then comes to the surface where the 

 fruiting body occurs. The l)ark of the Quaking Asp in the vicinity of 

 the fruiting body is of a blackish color. The fruiting bodies are at 

 first white, merely roundish knobs then become hoof shaped ; they con- 

 tinue to grow for several years each year adding a little more to the 

 old layers of the fungus. It is 3-6 inches long by 2 inches thick. The 

 surface of the fungus is brownish black and more or less cracked and 

 hard. The spores are colorless, spherical, 6-7m in diameter. 



Near Soldier Summit in the Wasatch mountains hundreds of trees 

 were attacked by the fungus, from small trees less than 6 inches to older 

 trees 8-12 inches in diameter. In many cases old trees were broken 

 down. It was apparent here that where one tree was diseased many 

 others could be found, and that the brackets on the surface were the 

 sources of infection. In other portions of the same region, as in the 

 Bear river country, Utah, the disease was not observed nor in the San 

 Miguel mountains in Colorado. 



The Oyster Fungus (Pleurotus ulmaritts Bull.) 



This fungus is common in many parts of Iowa and is to be re- 

 garded as a wound parasite, although not so active as the Fomes 

 igniarius. Common on the Box Elder and Basswood. Metcalf" men- 

 tions it as a wound parasite, stating that "presumably it does not 

 initiate the rot of the tree and certainly is not an active parasite like 

 the false tinder fungus, but it materially hastens the decay and ultimate 



"Die Zersetzungserscheinungen des Holzes. 



