66 Journal of Agricultural Research voi. in. No. i 



species the valuable white oak (Quercus alba) is commonly attacked. 

 To the east and north the fungus has been found less frequently, but it 

 occurs in many sections. 



From observations and estimates Polyporus dryophilus ranks with the 

 most common heart-rotting fungi which attack the oaks. In 191 2 the 

 senior writer found aspens {Populus treniuloides) in Colorado attacked by 

 this fungus. It apparently is not commonly found on this host. 



PIPED ROT CAUSED BY POLYPORUS DRYOPHILUS 



The whitish piped rot caused by Polyporus dryophilus has been found 

 by the writers to be directly associated with the sporophores of this fungus 

 in the following 15 species of trees: Quercus alba, 0. arizonica, Q. calijornica, 

 Q. digitata, Q. cmoryii, Q. gambclii, Q. garryana, Q. marilandica, 0. minor, 

 Q. prinoides, O. prinus, Q. texaita, 0. velutina, Q. virginiana, and Populus 

 tremidoides. 



PIPED ROT IN THE WHITE OAK 

 MACROSCOPIC CHARACTERS 



The first indication of the whitish piped rot in white oak is a discolora- 

 tion of the heartwood, which assumes a water-soaked appearance (PI. VIII, 

 fig. i). This "soak" may extend from i to 10 feet beyond the actually 

 rotting region where delignification is occurring. When dry, this water- 

 soaked heartwood becomes hazel to tawny in color. The next stage of 

 the rot is one of delignification, which usually begins alongside of and fol- 

 lowing more or less regularly the medullary rays, thus producing a mottled 

 appearance of the wood in radial view (PI. VIII, figs. 2, 5, and 6). This 

 type of the rot is very common in the medium-sized branches (6 to 12 

 inches in diameter) and in the early stages of the disease in the bole of the 

 tree. In final stages the diseased wood is firm, has a white, stringy ap- 

 pearance (PI. VIII, figs. 3 and 4) and consists of white cellulose strands of 

 delignified wood fibers and other wood structures bounded by areas of 

 apparently sound but actually slightly diseased and discolored heartwood. 

 Cinnamon-brown areas are scattered throughout the oldest rotted wood 

 (PI. VIII, fig. 3). These areas are especially common and abundant in the 

 vicinity of sporophores and along checks or openings through the sap- 

 wood. The rot immediately adjacent to a sporophore is therefore often 

 cinnamon brown to russet in color. No cavities large enough to be seen 

 by the naked eye are produced by this rot, but much of the white cellulose 

 is finally absorbed, leaving minute irregular cavities in the wood. 



MICROSCOPIC CHASACTERS 



Delignification usually begins in the wood fibers lying next to the vessels 

 in the spring wood and adjacent to the large medullary rays. The sol- 

 vents secreted by this fungus apparently are able to delignify all of the 



