A HONEYCOMB HEART-ROT OF OAKS CAUSED BY 

 STEREUM SUBPILEATUM 



By William H. Long, 

 Forest Pathologist, Investigations in Forest Pathology, Bureau of Plant Industry 



INTRODUCTION 



During investigations made in 191 2, 191 3, and 191 4 on the pathological 

 condition of the oaks (Quercus spp.) in the National Forests of Arkansas 

 and in other sections of the United States, the writer found a large 

 percentage of the trees, especially in some regions of Arkansas, attacked 

 by various species of heart-rotting fungi. Among this number were 

 several typical delignifying fungi : Polyporus pilotae; P. berkeleyi, and P. 

 jrondosus, which usually occur as butt-rots;^ and P. dryophilus, which 

 produces a widely distributed top-rot in oaks.^ In addition to the rots 

 produced by these' four fungi, another type of rot was found in oaks 

 which has certain characters not assignable to any fungus known to pro- 

 duce heart-rot in oaks. This undescribed rot is of the pocketed type 

 (PI. XLI, fig. i) and is a typical delignifier of the heart wood. In the 

 final stage of this rot the diseased wood resembles a piece of honeycomb 

 (PI. XLI, fig. 2). For this reason the writer calls it the "honeycomb 

 heart-rot." The rot is very similar to that produced by Stereum frus- 

 tulosum in dead standing or fallen oak timber, but is distinct from it. 



The writer has repeatedly found this rot directly associated with the 

 sporophores of 5. subpileatum. The mycelium could easily be traced 

 from the diseased wood to the subiculum of the sporophores. The only 

 sporophores of this fungus found were in direct association with the 

 typical honeycomb-rot. 



DESCRIPTION OF THE HONEYCOMB HEART-ROT 



The pocketed or honeycomb heart-rot caused by 5. subpileatum was 

 found by the writer to be directly associated with the sporophores of this 

 fungus in the following nine species of oaks: Quercus alba,^ Q. lyrata, O. 

 tnarilandica , Q. michauxii, Q. minor, 0. palustris, Q. iexana, 0. velutina, 

 and Q. virginiana. 



' Long, W. H. Three undescribed heart-rots of hardwood trees, especially of oak. In Jour. Agr. Re- 

 search, V. I, no. 2, p. 109-128, pi. 7-8. 1913. 



2 Hedgcock, G. G., and Long, W. H. Heart-rot of oaks and poplars caused by Polyporus dryophilus. 

 In Jour. Agr. Research, v. 3, no. i, p. 65-78, pi. 8-10. 1914. 



3 The nomenclature for trees used in this paper is that of George B. Sudworth. (Check list of the forest 

 trees of the United States, their names and ranges. U. S. Dept. Agr. Div. Forestry Bui. 17, 144 p. 1898.) 



Journal of Agricultural Research, VoL V. No. lo 



Dept. of Agriculture, Washington, D. C. Dec. 6, 1915 



av G— 67 



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