Murrill: Polypokaceae of North America 425 



thought to be responsible for the common name of " Sweet Knot," 

 by which it is known in some sections. 



The most common host of this species is the oak, especially 

 Quercus nigra ; but it also occurs on beech. The fruit bodies are 

 found on old dead trunks. 



Exsiccatae : Rav. Fung. Car. 3:8; Ell. N. A. Fung. 603 ; 

 Ohio, James, Cheney; Iowa, Maebride ; Pennsylvania, Sumstine. 



Nigrofomes gen. no v. 



Hymenophore large, perennial, epixylous, sessile ; context 

 woody, purple, tubes cylindrical, stratose, thick-walled, black ; 

 spores ovoid, smooth, hyaline. 



The type of this genus is Polyporus melanoporus Mont. (PI. Cell. 

 Cuba, 422. 1842), found on trunks of trees in tropical America. 

 The genus is readily distinguished from its near allies by its purple 

 context and black tubes. 



Nigrofomes melanoporus (Mont.) 

 Polyporus melanoporus Mont. PI. Cell. Cuba, 422. 1842. 



This species is the darkest-colored of the perennial polypores. 

 It was first described from collections made in Cuba by Ramon 

 de la Saera. Underwood has also collected it several times in 

 Jamaica and Florida and Smith has found it in Nicaragua. It is 

 probably more or less common throughout tropical America on 

 decaying trunks of various broad-leaved trees. 



Poronidulus gen. no v. 



Hymenophore annual, tough, sessile, epixylous, at first sterile 

 and cup-like, the fertile portion developing from the sterile ; con- 

 text white, fibrous, tubes short, thin-walled, mouths polygonal; 

 spores ellipsoidal, smooth, hyaline. 



The type of this genus is Boletus conchifer Schw. (Syn. Fung. 

 Car. 72. 1 8 18), a very common and abundant species on dead elm 

 branches. The development of the fruit-body is peculiar, being 

 in two stages, the first ending with the formation of a cup-shaped 

 sterile body, from which the fruit-body proper later develops. 

 This preliminary pileus begins as a knot of whitish mycelium, 



