486 CLASS BASIDIOMYCETEAE 



white margins and brown central portion on which the hymenium de- 

 velops. This rapidly becomes wrinkled and porose and sometimes in older 

 stages with flattened teeth much like those of Irpex. It occurs very 

 extensively over Europe and Asia but is comparatively rare in America. 

 Some species of MeruUus are laterally attached and form shelf -like spore 

 fruits. (Fig. 160.) 



Family Polyporaceae. The fungi here included in one family are 

 placed in two or more families by some of the more modern authors 

 (Rea, 1922; Donk, 1933; Singer, 1944). Until further studies show the 

 definite hmits of these different families it may be well to take the more 

 conservative stand and retain the one family. 



In the sense that the cells invaded by the hyphae of the fungi of this 

 family are mostly no longer Hving, i.e., wood fibers and tracheary tissue, 

 these fungi are saprophytes. Many of them, however, attack only the 

 sap wood of living trees in which living cells are intermingled with the 

 dead fiber and tracheary cells, bringing about a ''sap rot" and death of 

 the tree. Others, though confined to the heart wood, which contains few 

 if any living cells, attack this wood only in living standing trees. Still 

 others attack only the wood of dead trees or of structural timbers. So 

 there are all grades of practical parasitism even though the particular 

 cells invaded are not living. A very few species of this family are directly 

 parasitic upon other fungi. Although most species are wood inhabiting 

 some grow on the ground, obtaining their nourishment from buried 

 pieces of wood or from the vegetable matter in the soil. Such species are 

 true saprophytes. 



The spore fruits may be fleshy or fleshy-leathery when young but at 

 maturity are, with few exceptions, papery, leathery, corky, or even 

 woody. They range in size from a few millimeters in width and 1 or 2 mm. 

 in thickness to a width of 75 cm. (specimens of Ganoderma applanatum 

 (Pers. ex Fr.) Pat. collected by the author) and 30 to 50 cm. thick (speci- 

 mens of Fomitopsis (Fomes) officinalis (Vill.) B. & S. seen by the author), 

 and a width of over two meters in Polyporus squamosus (Huds.) Fr., 

 according to Clements (1910). They may be evanescent or may live 

 many years; according to Atkinson over 80 years in the case of specimens 

 of Phellinus {Fomes) igniarius (Fr.) Pat. 



The spore fruits may be closely appressed to the sides of tree branches, 

 logs, boards, etc., without a free margin, or may grow out laterally like 

 a shelf or bracket, or may be stalked laterally or centrally. The underside 

 is usually smooth when young, as in the Thelephoraceae, but develops 

 unevenly so as to leave numerous pits (pores) of various shapes on whose 

 inner face the hymenium develops. With but few exceptions the pores 

 are directed downward so that as the spores are shot off from the sterig- 

 mata of the basidia that line the pore they drop down and out of the 



