312 MANUAL OF TREE DISEASES 



surface. When fresh and soft, the lower surface turns brown 

 when bruised. When broken the inner substance is found to 

 be rusty brown and punky, with a distinct stratification of the 

 annually formed layers of tubes. A thicker and more ungulate 

 form with a black checked top and thin margin and a slightly 

 concave imder siuiace is commonly found growing from woimds 

 in the base of living oak trees. This form, while being classi- 

 fied under the same name as the typically flat sporophore, 

 differs greatly from it in general appearance and may represent 

 a closely related species or at least a distinct variety. 



Cause. 



White butt-rot of poplar, oak, beech and other deciduous 

 trees has been found to be caused by the bracket-fungus, Fomes 

 applanatus. Sporophores are formed near the base of the tree 

 at woimds or on exposed roots. The fruiting-bodies are peren- 

 nial, a new layer of tubes being formed on the under surface 

 each year. Infection seems to occur, usually, near the base of 

 the tree and the decay does not extend very far up into the trunk. 

 Trees in moist situations seem to be more often affected than 

 those on drier land. A general discussion of the life history 

 and control of the wood-rotting fungi will be found on page 64. 



References 



Heald, F. D. A disease of the eottonwood due to Elf vingia megaloma. 



Nebraska Agr. Exp. Sta. Ann. Rept. 19 : 92-100, pis. 1-4. 1906. 

 Hedgcock, G. G. Notes on some diseases of trees in our national 



forests. IV. Phytopathology 4 : 181-188. 1914. 



