Current Literature 66 



Heart-rot of Oaks and Poplars Caused by Polyporus dryo- 

 phihis. By George E. Hedgcock and W. H. Long. Reprint 

 from Jour. Agr. Research. U. S. Dept. Agr., Washington, D. C. 

 Vol. Ill, No. 1, 1914, pp. 65-77. 111. 



The larger and older oaks of the southwestern and western 

 United States are so affected by heart-rot that they are not used 

 to any extent for lumber and are, as a rule, valuable only for fuel. 

 The chief cause of this deterioration is Polyporus dryophilus, 

 which produces a whitish piped rot in the heartwood. The species 

 known to be attacked are Quercus alba, arizonica, calif ornica, digi- 

 tata, emoryii, gambelii, garryana, marilandica, minor, prinoides, 

 prinus, texana, velutina, virginiana, and Populus tremuloides. 

 The disease is very widely distributed, having been found in 

 twenty-three States and reported from several European 

 countries. 



The rots produced by this fungus in all the species of oak 

 examined had the following characters in common: (1) a water- 

 soaked, discolored area in the first stage; (3) a general associa- 

 tion of the earlier delignification with the medullary rays; (3) 

 later a more general delignification of all the wood fibers ; (4) the 

 formation of white mycelial lines; (5) the presence of cinnamon- 

 brown areas in the older rotted wood. 



It is interesting to note that "the cells of some of the medullary 

 rays and of the wood parenchyma often contain starch grains 

 even after the absorption of the inclosing cell walls," thus proving 

 that it is the cell wall rather than the contents which is the 

 primary object of attack. 



Polyporus dyrophilus is believed to gain entrance into the wood 

 of the host trees only through wounds in which the heartwood is 

 exposed, such as broken or dead limbs and fire scars. When it 

 enters the stub of a limb it grows downward through the heart- 

 wood to the trunk and spreads both upward and downward 

 through the heart of the tree. When it enters a basal wound 

 it sometimes spreads upward throughout the heart of the entire 

 trunk. In the aspen the fungus will attack the living sapwood 

 when the disease becomes far advanced. 



S. J. R. 



