424 Journal of Agricultural Research 



Vol. V. No. 10 



or less tough, brown mycelial weft in the fissures of the wood. A similar 

 mycelial growth often develops on specimens of freshly cut rotting wood 

 from the exposed edges of the cellulose-filled cavities and may even over- 

 run the surface of the rotting wood for several square inches. 



This reddish growth seems to occur only when the actively growing 

 hyphag are exposed to the air, since in the interior of the wood, where 

 they are not thus exposed, the mycelium lining the original cavities caused 

 by this fungus is white. The brownish mat of mycelium which forms in 

 the fissures of the wood consists of dense interwoven masses of sparingly 

 septate, fulvous h3^phae. The clamp connections of these hyphae are not 

 very pronounced, in marked contrast to those of 5. frustulosum. These 

 hyphae are from 2 to 3/i thick, as a rule, but smaller ones are not 

 uncommon with branches putting out at right angles to the main hypha. 

 The outer walls of some of the hyphae are sparingly granular to almost 

 tuberculate. 



The very old pockets are often filled with a brownish floccose mass, 

 which is composed of brown, tuberculate hyphae similar to those seen in 

 the rot produced by S. frustulosum. 



RESEMBLANCE OF THE ROT CAUSED BY STEREUM SUBPILEATUM TO 

 CERTAIN OTHER ROTS 



It is very difficult and often impossible to separate very similar types 

 of rot from one another, unless the fruiting bodies of the causative 

 organism are present in direct association with the rot. 



There are four delignifying heart-rots which are very similar in certain 

 stages of their development to each other and to portions of the descrip- 

 tion given by Von Schrenk and Spaulding ^ of a piped-rot of oak and 

 chestnut. In the light of recent investigations these four rots are now 

 known to be caused by the following fungi : (i ) Polyporus dryophilus, which 

 causes a very common heart-rot in the upper portion of the trunks of 

 oaks in the United States and is found occasionally in poplars; (2) 

 P. pilotae, which attacks the heartwood of oaks and chestnuts; (3) 

 Stereum subpileatum, which causes a pocketed-rot of oaks; and (4) 

 Hymenochaete rubiginosa, which causes a pocketed-rot in chestnut and 

 oak. The writer has specimens of the last-named fungus, collected 

 during the past three years in several States and associated with a 

 delignifying pocketed heart-rot in living chestnut. On account of the 

 meagerness of the sporophore material, the writer was uncertain whether 

 H. rubiginosa was really the cause of the rot with which it was associated 

 or was only a secondary fungus on already diseased chestnut timber. 

 Brown in a recent article ^ describes a pocketed-rot in dead chestnut and 

 oak timber wnth which the sporophores of H. rubiginosa are constantly 

 associated. However, he did not find it as a heart-rot in living trees. 



1 Schrenk, Hermann von, and Spaulding, Perley. Diseases of deciduous forest trees. U. S. Dept. 

 Agr. Bur. Plant Indus. Bui. 149, S5 p., 11 fig., 10 pi. 1909. 



2 Brown, H. P. A timbcT rot accompanying Hymenochaete rubiginosa (Schrad.) Lev. In Mycologia, 

 V. 7, no. I, p. 1-20, pi. I49r-i5i. 1915. 



