96 MANUAL OF TREE DISEASES 



white, while for a time the summer-wood remains brownish. 

 Shortly, however, the summer-wood becomes whitish and in 

 the final stages of the decay the wood is soft and crumbly. 



The perennial sporophores of the causal fungus are formed 

 at old branch woimds. They are usually small bracket-shaped 

 bodies. The upper surface is hard, dark brown or black and 

 marked by concentric folds. The under surface is velvety, 

 straw-colored and covered with large circular pores. The 

 inner structure of the fruiting-body is white or light brown, 

 according to its age. A new layer of tubes is added to the 

 lower surface each year. 



Cause. 



The white heartwood-rot of white ash is caused by Fames 

 fraxinophiliis. This fungus is rarely found on any other tree. 

 Living green ash trees have been observed with the fruiting- 

 bodies on them and it is possible that a rot of similar nature as 

 that caused in white ash may be found in green and other ashes. 

 The spores borne within the tubes on the under surface of the 

 fruiting-body fall out of the pores and are blown about by the 

 wind. When they find lodgment on exposed heartwood of the 

 white ash, a new mycelium may be initiated. The initial 

 stages in the decomposition of the fibers result in a brown 

 liquid which stains the wood. Later this colored liquid disap- 

 pears and the mycelium delignifies the cell-walls and dissolves 

 most of the cellulose. The fungus is not known to occur as a 

 saprophyte. For further details concerning the life history and 

 control of the wood-rotting fungi of living trees, see page 64. 



References 



Sohrenk, Hermann von. A disease of the white ash caused by Poly- 

 porus fraxinophilus. U. S. Dept. Agr. Bur. PI. Ind. Bui. 32: 

 1-20, pis. 1-5, fig. 1. 1903. 



Sohrenk, Hermann von, and Spaulding, P. White heart-rot of ash 

 caused by Pomes fraxinophilus. In Diseases of deciduous forest 

 trees. U. S. Dept. Agr. Bur. PI. Ind. Bui. 149 : 4&-47. 1909. 



