Dec. 6,1915 Honeycoynh Heart-Rot of Oaks 425 



COMPARISON OF ROTS OF STEREUM SUBPILEATUM AND POLYPORUS PILOTA© 



In the writer's investigation in the Ozarks no attempt was made in 

 the field to separate the rot caused by P. pilotae from that caused by 

 S. suhpileatum, since both in their early stages produce small delignified 

 areas in the diseased heartwood of living trees. It was therefore difficult 

 to determine which fungus produced the rot unless the sporophores were 

 present. Attention was called to this resemblance in a previous article 

 by the writer.^ However, the final stage of the rot produced by P. 

 pilotae is quite distinct from that of 5. suhpileatum. The rot caused 

 by P. pilotae usually moves upward in the infected wood, along certain 

 well-defined zones consisting of several annual rings of growth of the 

 wood. These zones are usually separated by zones of apparently ^ound 

 tissue — that is, the rot moves upward or longitudinally in the tree 

 more rapidly than it does radially. The rot caused by 5. subpileatum 

 does not seem to form definite zones of infected wood separated by 

 sound zones, at least in the white oak, but seems to move as rapidly 

 radially as longitudinally in the attacked heartwood, thus forming a 

 uniform cylinder of rotted wood in the heartwood of the trees. If 

 this character should prove constant, one could use it in field work 

 for differentiating this rot from the earlier stages of the rot of P. pilotae. 

 However, in well-advanced stages of rot, the presence of typical lens- 

 shaped to cylindrical pockets occupying practically all of the infected 

 heartwood is fairly indicative that the rot in question is caused by 5. 

 subpileatum. 



ENTRANCE OP THE FUNGUS INTO THE HOST 



The fungus 5. subpileatum, so far as the writer knows, enters the wood 

 of the hosts only through wounds which expose the heartwood. The 

 most common point of entrance is through wounds, usually fire scars, 

 in the butt of the trees, although it also frequently enters through 

 branch stubs. The writer found this rot several times in the tops of 

 living white-oak and black-oak trees in the Ozark National Forest, 

 Arkansas. In every case the fungus had undoubtedly entered through 

 a branch stub. It produces the same type of rot (PI. XLI, fig. 4 and 

 7) in the tops as it does in the butts, even to the peculiar honeycomb- 

 like odor. 



No instances were found where this rot had entered a living tree 

 through the dead sap wood of a wound, nor where it had entered a dead 

 tree or log through the sapwood. It is very probable, however, that 

 the fungus does attack dead timber in this manner, since many examples 

 were found where the fungus had grown from the heartwood into the 

 dead sapwood of felled trees. 



'Long, W. H. Three imdescribed heart-rots of hardwood trees, especially of oak. hi Jour. Agr. 

 Research, v. i, no. 2, p. 109-128, pi. 7-R. 1913. 



