348 THE BASIDIOMYCETES 



parts of the world have given these fungi critical study. Accord 

 has not been reached on generic and specific limits, as is evident 

 from the fact that Murrill (1907-1908) recognizes 78 genera of 

 North American polvpores, whereas others reduce this number 

 to less than 20. Among the structural features which appear to 

 constitute rational bases for generic distinction are: (1) consist- 

 ency of the fructification, whether fleshy, gelatinous, leathery, 

 corky, or woody; (2) shape of the fructification, whether resupi- 

 nate, effuse-reflexed, bracket-like, applanate, ungulate, or stipi- 

 tate; (3) shape of the pores, whether circular, angular, labyrinthi- 

 form, daedalioid, or lamelliform; (4) nature of the pore layer, 

 whether the pores are separable from the context (tissue of the 

 pileus), whether the tissue of the pileus extends between the 

 pores, w^hether the pores are shallow corrugations or well-defined 

 pores, whether the pores are separate peg-like tubes, or whether 

 their contiguous walls are united. 



The Polyporaceae may rather conveniently be divided into 

 the following 4 tribes, according to Hennings: 



a. Basidiocarp effuse, at first plane but having fold-like elevations 



which anastomose to make shallow and irregular pits Meruleae 



a. Basidiocarp having tubes, alveolar areas, labvrinthiform passages, 

 or radiating lamellae 



b. Substance of the hymenium continuous with dissepiments of 

 the tubes; tubes not readilv separable from the context (hy- 

 menophore) 



c. Tubes closelv contiguous Polyporeae 



c. Tubes standing sins^lv Fistulineae 



b. Substance of hvmenium easily separable from the hvmenophore 



Boleteae 



Meruleae. Aienilhis lacrymans, \\'hich typifies the genus, 

 causes dry rot of woodwork in buildings. Extension of the 

 fungus is accomplished by fibrous rhizomorphs. It forms wide- 

 spreading gelatinous to cartilaginous fructifications that are re- 

 ticulately folded or corrugated. Burt (1917) found that the ba- 

 sidia are mature while the hymenial surface is still plane and that, 

 by subsequent growth, folds appear; thus the basidia clothe the 

 edges of the folds as well as the sides and bottom. In other 

 Polyporaceae the pores are formed in advance of the maturation 

 of basidia; hence some workers would exclude Merulius from 

 this family. 



