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 1912, 1913, and 1914 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 delignifyingfungi: Poly poms pUotae; P. berkeleyi , and P. 
frondosus , which usually occur as butt-rots; 1 and P. dryophilus , which 
produces a widely distributed top-rot in oaks. 2 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 
(PL XU, fig- 1) and is a typical delignifier of the heartwood. In the 
final stage of this rot the diseased wood resembles a piece of honeycomb 
(PL XL I, 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 . subpUeatum . 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 S. subpUeatum 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 , Q . 
marilandica , Q. michauxii, Q. minor , Q. palustris , Q. texana, Q. velutina , 
and Q. virginiana. 
1 Long, W. H. Three undescribed heart-rots of hardwood trees, especially of oak. In Jour. Agr. Re¬ 
search, v. r, 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. 1, 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, 
Dept, of Agriculture, Washington, D. C. 
av 
(421) 
VoL V. No. 10 
Dec. 6, 1915 
G-67 
