424 THE FUNGI WHICH CAUSE PLANT DISEASE 



bay-brown, at first minute, circular, becoming angular, 4 to a 

 mm., edges thin, fimbriate to lacerate, deeply splitting and 

 separating with age: spores subglobose, smooth, &-10 x 7-8 m» 

 the outer wall hyaline, the inner membrane brown; cystidia 15- 

 35 X 6-9 M. 



It causes rot of oak wood in America and Europe. 



P. amarus Hedg.*^- *^* 



Pileus soft and spongy when yoimg, becoming hard and chalky 

 when old, ungulate, often spuriously stipitate from knot-holes, fre- 

 quently large, 5-11 x 10-20 x 6-12 cm.; surface pubescent when 

 yoxmg, rimose and chalky when old, at first buff, becoming tan 

 and often blotched with brown when older; margin obtuse, fre- 

 quently having an outer band of darker brown, often slightly 

 furrowed; context creamy-yellow to tan-colored, usually darker in 

 outer layers when old, 4-8 cm. thick; tubes not stratified, brown 

 within, cylindric, 0.5-3 cm. in length, shorter next the margin, 

 mouths circular or slightly irregular, 1-3 to a mm., yellow-green 

 during growth, turning brown when bruised or old, becoming 

 lacerate; spores hyaline or slightly tinged with brown, smooth, 

 ovoid, 3-4 X 5-8 ii, nucleated; cystidia none. 



The cause of "pin rot" or peckiness of incense cedar. 



P. schweinitzii Fr.^*' " 



Pileus spongy, circular, varying to dimidiate or irregular, 15-20 

 cm. broad, 0.5-2 cm. thick; surface setose-hispid to strigose- 

 tomentose and scrupose in zones, ochraceous-ferruginous to ful- 

 vous-castaneous or darker, quite uneven, somewhat sulcate, ob- 

 scurely zonate; margui yellow, rather thick, sterile: context very 

 soft and spongy, fragile when dry, sometimes indurate with age, 

 flavous-ferruginous to fulvous, 0.3-0.7 mm. thick; tubes short, 

 2-5 mm. long, fiavous within, mouths large, irregular, averaging 

 1 mm. in diameter, edges thin, becoming lacerate, ochraceous- 

 olivaceous to fuliginous, rose-tinted when young and fresh, quickly 

 changing to dark-red when bruised: spores ovoid, hyaline 7-8 x 3-4 

 ju: stipe central to lateral or obsolete, very irregular, tubercular 

 or very short, resembling the pileus in surface and substance. 



On coniferous trees especially spruce, fir, pine, larch, arbor vitaj, 

 entering through the root system and extending up the trunk, 

 causing heart-rot. The tracheids exhibit spiral cracks and fissures 



