THE FUNGI WHICH CAUSE PLANT DISEASE 423 



Fig. 303. — Polyporus Ito- 

 realis, hymenium with 

 sinuous pores. After At- 

 kinson. 



p. boreaHs (Wahl.) Fr."- ^® 



Pileus sessile, subimbricate, dimidiate to flabellifonn, often 

 narrowly attached, spongy to corky, very tough, moist and juicy 

 when fresh, 5-8 x 8-12 x 2-4 cm.; surface uneven, soft and spongy, 

 hirtose-tomentose, azonate, white to yellowish; margin thin, white, 

 entire, somewhat discolored on drying: 

 context fibrous-coriaceous above, fibrous- 

 woody below, white, 0.5-1.5 cm. thick; 

 tubes 4-8 mm. long, white to pallid within, 

 mouths angular, irregular, somewhat 

 radiately elongate, sinuous at times, 1-2 

 to a mm., stuffed when young, edges thin, 

 white to ochraceous, dentate to lacerate; 

 spores ovoid, smooth, hyaline, 5-6 x 3^ fi; 

 hyphiE 6-7 fj,; cystidia none. 



On pine, spruce, hemlock, balsam pine, 

 etc., as a wound parasite or as a sapro- 

 phjrte on dead trees producing a white rot. The mycelium ad- 

 vances longitudinally, radially and tangentially. At certain 

 stages it is very abundant and forms cords in the channels formed 

 by the fungous enzyme. Later these cords disappear. The young 

 mycelium is stout and yellow, later it is more delicate. Dis- 

 solution of the cells begins at the lumen 

 and proceeds outward, the middle lamella 

 persisting last. 

 P. dryadeus Fr." 



Sporophore very large, sessile, dimidiate, 

 rarely circular, usually imbricate, applanate 

 or depressed above, convex below, fleshy to 

 spongy-corky, rather fragile when dry, 15- 

 30 X 25-65 X 3-5 cm.; surface very un- 

 even, azonate, opaque, hoary-isabelline, 

 anoderm to very thinly encrusted, sub- 

 shining and bay; margin thick, pallid, entire to imdulate, weep- 

 ing; context thick, zonate, subglistening, ferruginous-isabelline to 

 fulvous, 2.5-4 cm. thick; tubes grayish-umbrinous to fulvous 

 within, 5-15 mm. long, slender, very fragile, mouths whitish when 

 young, becoming somewhat resinous in appearance and finally 



5S 



Fig. 304. — Polyporus bo- 

 rcalis, hymenium with 

 rounded pores. After 

 Atkinson. 



