78 PRACTICAL TREE REPAIR 



aged. They very quickly attack unseasoned tim- 

 ber, standing or felled. For instance, Polystictus 

 pergamenus is frequently found growing on trees 

 which have been seriously injured by fire, frost, 

 or sunscald. It attacks the .dead bark first, 

 spreading later into the sapwood. In a few years 

 it sends out hundreds of little shelf-like, leathery 

 sporophores. The prompt cleaning away of every 

 patch of dead bark and the dressing of wounds 

 are the only preventive measures, and of course 

 complete excision is the only cure. 



The third group is the most important of all. 

 Almost all its members are wound rots, entering 

 the tree through exposed surfaces of wood. 

 They make their way from the wounded spot into 

 the heart of the tree, and grow up and down in 

 the heartwood. The destruction of the heart- 

 wood is not immediately harmful to the tree, and 

 some fungi cannot spread outside of the heart- 

 wood. Others, the majority, though they cannot 

 actually invade healthy sapwood vessels, can work 

 their way into the sapwood by virtue of certain 

 changes, approximating a change into heartwood, 

 which take place in the sapwood immediately con- 

 tiguous to the decay. These changes take place 

 most readily where the sapwood has become drier 

 than usual, as through the death of a root just be- 

 low it, or the removal of the bark covering it. 

 Thus the fungus can work its way to the surface 



