Oct. 15, 1914 Heart-Rot of Oaks and Poplars 71 



States, in every instance shows this hard granular core (PI. IX, figs. 2 

 and 4) exactly as figured and described by Hartig (1878) in case of his 

 P. dryadeus. This core extends back some distance into the tree in 

 oaks; it is usually irregularly cylindrical while in the tree, but on its 

 emergence from the tree it swells into a tuberous or spheroid mass and 

 finally occupies the central and rear part of the sporophore (Pis. IX, fig. 2, 

 and X, fig. 6). If the sporophore is formed from a large branch hole, 

 it is usually of the applanate type, with a small core, but when the sporo- 

 phore forms directly on the body of the tree, as it usually does, the shape 

 is tuberous, unguliform, or even subglobular (PI. IX, figs. 2 and 4), with 

 the bulk of the sporophore composed of hard, granular core. This core 

 usually has white mycelial strands (PI. IX, fig. 4). The sporophore of 

 P. dryophilus, therefore, has normally three distinct kinds of structures 

 (PI. X, fig. 4): (i) The hard, granular core; (2) the fibrous layer which 

 surrounds this core except at the rear; (3) the layer of tubes on the lower 

 surface. Specimens are often found, however, especially from the 

 western part of the United States, in which this fibrous layer may be 

 entirely absent between the tubes and the granular core (PI. IX, fig. 4). 



Polyporus dryophilus is known in Europe under at least five different 

 names: Polyporus julvus Fries, P. friesii Bresadola, and P. corruscans 

 Fries for the form on oak, and P. ridpinus Fries and P. rheades Persoon 

 for the form on poplar. The identity of P. dryophilus with the P. cor- 

 ruscans Fries (PI. X, fig. 4) and with P. rheades Persoon is based on the 

 specimens of these plants found in the Lloyd Herbarium at Cincinnati, 

 Ohio. If these specimens are correctly determined, then the American 

 plant is identical with the European plants named above. Authentic 

 specimens of the form of P. dryophilus found on species of Populus were 

 seen by the junior writer at the New York Botanical Gardens in collec- 

 tions from Finland and Sweden and also from Maine. In the Lloyd Her- 

 barium at Cincinnati, Ohio, are collections under the name of P. rheades 

 on Popidus trcmida from Sweden (PI. X, fig. 3) and Denmark, and a 

 collection from Austria on Quercus ilex. In the Cryptogamic Herbarium of 

 Harvard University there is a collection on Populus grandidentata Michx. 

 from New Hampshire, while in the Laboratory of Forest Pathology there 

 is a fine collection on Populus tremuloidcs Michx. (PI. X, figs, i, 2, and 5) 

 from near Steamboat Springs, Colo. 



This fungus on Populus agrees in all essential characters with the form 

 of Polyporus dryophilus found on oak. The sporophores are, however, 

 somewhat smaller than those usually found on oak and approach the 

 applanate type (PI. X, figs, i and 2). The hard granular core is always 

 present, but is formed between the sapwood and bark (PI. X, fig. 4), as 

 the fungus is able to rot the sapwood, as well as the heart of this host. It 

 therefore does not have to depend on branch holes or other openings 

 through the sapwood in order to form its sporophores as it does in the 

 oak. 



