CHAPTER V 



HEART-ROT. FOMES ANNOSUS 



Various fungi which cause heart-rot. Fomes annosus : general ; his- 

 torical. Secretions induced by Fomes annosus : turpentine and resin ; 

 soluble gum ; insoluble gum. Decomposition of the wood. 



HEART-ROT of trees is caused by fungi which grow sapro- 

 phytically on the dead wood, but are cither incapable of 

 growing parasitically, or attack living tissues very feebly. 

 The heart-wood of trees is dead, has lost all its protoplasm 

 and with it much of its power of resisting fungi. Though 

 it is more resistant than dead sap-wood, it is by far the 

 most susceptible part of the trunk of a living tree, and 

 is liable to become entirely decayed, leaving only a ring of 

 healthy sap-wood which maintains the life of the tree. 

 With the destruction of the heart-wood the tree may lose 

 none of its vital activity, but it is nevertheless weakened 

 in two respects. The central column of tough wood is lost 

 and the tree is much more liable to be wind-blown, especially 

 as the roots are often weakened in the same manner as the 

 trunk, and if the central hollow has any communication 

 with the outside air, a ready means of infection is provided 

 for truly parasitic fungi. 



One of the most familiar instances of heart-rot caused 

 by a purely saprophytic fungus is afforded by the elm. 

 This tree is usually grown in avenues or hedgerows where 

 large lateral branches are allowed to develop which would 

 be suppressed*in closely -timbered woods. These branches 

 are brittle, and frequent breakages result in numerous large 

 scars which expose both sap-wood and heart- wood to fungal 

 attack. In summer spores are nearly everywhere present 

 to take advantage of these scars, and the trees become 

 infected with such fungi as Fomes ulmarius, which is the 

 chief, if not the only, cause of heart-rot and hollowness in 



