THE FUNGI WHICH CAUSE PLAxNT DISEASE 419 



It causes a heart-rot of living oaks, occurring as a wound parasite 

 and invading the sap wood when decay is well advanced. It is 

 also found on black locust/'^ 

 P. sulphureus (Bui.) Fr."' "• '«• ''■ "• «" 



Hymenophore cespitose-multiplex, 30-60 em. broad; pileus 

 cheesy, not becoming rigid, reniform, very broad, more or less 

 stipitate, 5-15 x 7-20 x 

 0.5-1 cm. ; surface finelj 

 tomentose to glabrous, 

 rugose, anoderm, sub- 

 zonate at times, vary- 

 ing from lemon-yellow 

 to orange, fading out 

 with age; margin thin, 

 fertile, concolorous, 

 subzonate, finely to- 

 rn e n to s e, undulate, 

 rarely lobed; context 

 cheesy, very fragile 

 when dry, yellow when 

 fresh, usually white in 

 dried specimens, homogenous, 3-7 mm. thick; tubes annual, 

 2-3 mm. long, sulphur-yellow within; mouths minute, angular, 

 somewhat irregular, 3^ to a mm., edges very thin, lacerate, 

 sulphur-yellow, with color fairly permanent in dried specimens; 

 spores ovoid, smooth or finely papillate, hyaline, 6-8 x 3-5 ju. 



It is common as a cause of red heart-rot of forest and shade 

 trees, conifers and deciduous, and also does damage in the orchard, 

 especially on cherry, apple and pear, and in the forest to oak, chest- 

 nut, poplar, maple, walnut, butternut, alder, locust, ash, pine, 

 hemlock, larch. 



The decayed wood resembles a mass of red-brown charcoal and 

 is characterized by radial or concentric cracks in which the fungus 

 forms thin leathery sheets. In dicotyledons the vessels become 

 filled with the fungus. Round gonidia are often formed within 

 the wood. 

 P. squamosus (Huds.) Fr. "• "• " 

 Sporophore of immense size, reaching 50 cm. in breadth and 3 cm. 



Fig. 300. — Polyporus sulphureus. Scattered fruit 

 bodies on living oak. After Atkinson. 



