74 PRACTICAL TREE REPAIR 



section of a rotted trunk, between the diseased 

 wood and the sound wood. Sometimes the wood 

 is discolored before it is actually invaded. In 

 other forms, the wood is invaded a considerable 

 distance before any change is 

 observable to the unaided eye. 

 When a fungus is working up 

 a tree, also, it often sends an 

 advance guard of mycelium 

 up the very center of the 

 trunk, where the soft pith 

 makes its progress easy. All 

 these facts make it much more 

 difficult than it would other- 

 wise be to make a complete 

 excision of decayed wood. 

 As regards the rate at 

 which decay spreads through wood, but little is 

 definitely known. It is certain that different de- 

 cays grow at different rates, and that the same 

 decay spreads at different rates in different trees. 

 The indications are that, in the main, de- 

 cays spread very slowly — sometimes only a little 

 faster than the wood is built up by the cambium. 

 After the passage of a greater or less period of 

 time, often amounting to many years, a denser 

 mass of hyphas than usual gathers at some point 

 near the outer surface of the host, usually at a 

 wound, a rotted knot-hole, or the burrow of a 



Section of a decayed 

 trunk, showing rela- 

 tion of sporophore to 

 decay 



