114 SHADE TREES. 



oaks, red gum, maples, birch, chestnut, hickory, tulip, poplar, 

 black cherry, beech, willows and others, especi- 



Attaeks in- i i i i 



jured trees ally those that have been injured, and is widely 

 distributed throughout 2s"orth America. How- 

 ever, it has been questioned whether this fungus ever occurs 

 on the living parts of trees. The general appearance of the 

 decay is very similar to that caused by P. versicolor. (Fig. 

 42.) The fruiting bodies are leathery, generally white when 

 young but growing gray with age, the upper surface slightly 

 hairy and the lower surface purplish; the pores are small 

 and tend to produce a ragged surface with a.2;e. 



Treatment. 



Protection from injury and the proper care of wounds 

 will practically prevent the occurrence of this disease. 



P. betulinus (Bull) Fr. is the cause of a sap rot on several 

 species of birch and other trees, but whether parasitic or 

 saprophytic is a disputed point. The same is true of P. 

 fomentarius (L.) Fr. 



Fomes applanatus (Pers.) Wallr., one of the most con- 

 spicuous of our shelving fungi is said to cause a sap rot 

 disease on cottonwoods. However, on most trees it must be 

 considered purely saprophytic. 



There are a large number of other sap rots 



he e a e ithyf es due to a number of species of fungi occurring 



on many species of trees. Most of them are 



saprophytic, but some of them are or may become parasitic, 



especially on trees which are weakened from other causes. 



3. DISEASES OF THE ROOTS. 



The diseases of roots are very imperfectly understood. 

 They may be due to unfavorable soil conditions, or to fungi, 

 or to both. Probably the most important of these diseases is 

 the rot due to the fungus Armillaria mellea (Vahl.) Que- 



