THE POLYPORACEAE OF WISCONSIN. 85 



The form growing on maple, elm and birch is the type-form and is 

 easily recognized by the black rimose surface. The largest of these 

 measured 12 cm. in width, 9 cm. in length and 3 cm. in thickness. The 

 shape is, however, very variable. Another specimen measured about 

 10 cm. in length, 10 cm. in width and 15 cm. in thickness. This speci- 

 men grew from the trunk of a living rock elm and had 22 strata. It 

 is quite common on living elm and birch at Shanagolden. 



The usual form which grows on dead or living poplar is quite dif- 

 ferent. It is duller in color, and irregularly orbicular. The largest 

 specimens being about 9 cm. long, 9 cm. wide and from 3 to 5 cm. 

 thick. Many grow immediately beneath small branches, along which 

 they spread upwards a distance of 10 or 12 cm., thus appearing resupi- 

 nate, but in nearly all cases the lower surface is ascending, never hori- 

 zontal. They also grow into, and push up the bark of the trunk so 

 that it is difficult to tell where the bark ends and the fungus begins, for 

 the color of the top of the pileus is very much like that of the bark. 

 This color is an opaque grayish-black instead of a varnished black. 

 Below, the fungus is a dark cinnamon brown. The substance and the 

 tubes are also dark cinnamon brown and very hard. The surface is 

 densely sulcate and much checked. The margin is smooth, gray, and 

 where the hymenium meets it, brown. It is quite obtuse in resupinate 

 forms but more acute in others. In cross-section these specimens are 

 always triangular. Sometimes young specimens are nodular with a 

 thick, brown rounded margin like our F. igniarius; but the forms can 

 usually be distinguished from the latter by their intimate connection 

 with the bark, and by the darker, harder and more brittle substance 

 which is only faintly zonate. 



The tubes are small, stratose and not more than about 5 mm. in 

 length, soon becoming white stuffed. The pores are extremely small, 

 roundish, regular, with thick dissepiments. Since this form is quite con- 

 stant and easily distinguishable I shall describe it as a variety. 



Fomes nigricans populinus n. var. 



Irregularly orbicular or sessile, triangular, opaque, rugose, radially 

 rimose with very small pores, common and abundant on poplar. 



The above species, especially the variety, is closely related to F. 

 igniarius, but can usually be distinguished by its habit of growth and 

 by its hard, black, densely rimose surface. The substance of the pileus 

 is never as thick as that of F. igniarius. 



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