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



PIPED ROT IN EUROPEAN OAKS 



Robert Hartig (1878), in his epoch-making work on the true nature 

 of the rots of woods, described a whitish heart-rot of the oak, which he 

 attributed to Polyporus dryadeus. A careful study of Hartig's figures, 

 and the description of the sporophore which he found associated with 

 the white heart-rot so accurately described by him, is sufficient to con- 

 vince anyone who is familiar with the true P. dryadeus that Hartig's 

 fungus was not P. dryadeus. It is undoubtedly identical with the 

 heart-rotting fungus known in America as P. dryophilus and found by 

 the senior author to be associated with a whitish piped rot in oak. 

 Through the kindness of Dr. Von Tubeuf the junior writer obtained a 

 piece of the original rot (PI. VIII, figs. 7 and 8) which Robert Hartig (1878) 

 ascribed to P. dryadeus. A careful study of this specimen showed that 

 it is identical in every respect with the rot produced by P. dryophilus 

 in the white oak. There is also another European specimen (PI. VIII, 

 fig. 9) of this rot in oak in the Laboratory of Forest Pathology, of the 

 Department of Agriculture, which has all the characters of the rot pro- 

 duced by P. dryophilus . 



CHARACTERS OF PIPED ROT COMMON TO ALL SPECIES OF OAKS 



The rots produced by Polyporus dryophilus in all the species of oak 

 examined had the following characters in common: (i) A water-soaked 

 discolored area in the first stage (PI. VIII, fig. i) ; (2) a general association 

 of the earUer delignification with the medullary rays (PI. VIII, figs. 5 

 and 6) ; (3) later a more general delignification of all the wood fibers 

 (PI. VIII, fig. 3) ; (4) the formation of white mycelial longitudinal lines 

 (PI. VIII, fig. 4); (5) the presence of cinnamon-brown areas in the older 

 rotted wood (PI. VIII, fig. 3). These brown patches, ranging from 2 by 4 

 mm. up to 10 by 35 mm. in size, consist of fragments of wood interwoven 

 with ferruginous, thick-walled, septate hyphae, which easily break into 

 short pieces. The hyphae are about 3// thick, have many short (3 to 8;u) 

 branches, and are mixed with various sizes of hyphae down to i/x or less 

 in diameter, the smaller of which are hyaline. 



HEART-ROT PRODUCED BY POLYPORUS DRYOPHILUS IN ASPEN 



The description of the heart-rot which follows was made from the 

 diseased wood of a dead aspen {Populus tremuloides) bearing the sporo- 

 phores of Polyporus dryophilus . 



MACROSCOPIC CHARACTERS 



The general color of the diseased wood varies from a light buff to a 

 maize yellow. In a cross section the rotted wood shows alternating 

 concentric zones of light buff and ochraceous tawny. The light-colored 

 zones consist of the vessels and wood fibers which have been the most 

 vngorously attacked by the solvents of the fungus. The ochraceous- 



