BIRCH DISEASES 115 



Cause. 



The powdery sapwood-rot of birch is caused by Polyporus 

 hetulinus. The spores borne in the tubes on the under side 

 of the sporophore cause infection in wounds where the sapwood 

 is exposed. For a fuller discussion of the life history and control 

 of wood-rot fungi, see page 64. 



References 



Sehrenk, Hermann von, and Spaulding, P. Decay caused by Poly- 

 porus betulinus. In Diseases of deciduous forest trees. U. S. 

 Dept. Agr. Bur. PI. Ind. Bui. 149 : 51-52, pi. 9. 1909. 



Mayr, H. Zwei Parasiten der Birke, Polyporus betulinus, BuU., 

 and Polyporus lavigatus. Fries. Bot. Centralbl. 19 : 22-29, 51- 

 57, pi. 1-2. 1884. 



Yellowish Sapwood-Rot 



Caused by Forties fomentarius Fries 



Yellow birch and beech are commonly affected by this sap- 

 wood-rot. Other kinds of deciduous trees are sometimes 

 attacked. The sporophores are perennial, light or dark gray 

 above, smooth and hoof-shaped with a concave, brown, velvety 

 tube-layer. The sapwood is decayed and only an easily 

 crumbled mass of fibers is left. A more complete description 

 of the symptoms of this wood-rot is given under beech 

 diseases, page 105. 



Common White Wood-Rot 



Caused by Fames igniarius Fries 



The common and destructive white wood-rot of poplar, 

 beech, oak, maple and other deciduous trees affects the yellow 

 and paper birch. Although not as prevalent on birch as on 

 many other kinds of trees, it is often found, especially when 

 the birches are growing in mixture with the more susceptible 



