POLYPORUS 379 



narrow dark brown zone indicates the outward progress of 

 the mycelium, and outside this band appears to be healthy, 

 but a careful microscopic examination of the apparently sound 

 wood reveals the presence of delicate strands of mycelium, 

 which gradually extends towards the surface'of the trunk ; the 

 brown zone in like manner is constantly advancing. 



Often imbricated; pileus bracket-shaped, more or less 

 semicircular, attached by a broad base, rather flat and not 

 hoof-shaped, pileus rusty-brown, coarsely hispid, flesh spongy- 

 fibrous, rusty ; tubes J to i in. long, yellowish-green, then 

 brownish, pores minute, spores elliptic, orange-brown, 10 x 7 /*. 



Pileus 4 in. to a foot across. Often very dark when old. 

 When actively growing the tubes exude water which drips, 

 carrying the spores along with it in considerable quantities. 

 Every part of the fungus yields a deep yellow colouring 

 matter fungus gamboge, when soaked in spirit or in an 

 alkaline solution. 



Preventive measures, the same as given under allied 

 species. 



Prillieux, Ed., Maladies des Plantes Agricoles> i, p. 352 



Birch polyporus (Polyporus betulinus. Fries.) is exceedingly 

 abundant on birch-trees in this country, and when a consider- 

 able number of sporophores are present on a trunk the effect 

 is certainly very artistic ; to appreciate this to the fullest 

 extent a visit should be paid to the old birch woods forming 

 part of Sherwood Forest. The fungus is a wound-parasite, 

 the mycelium produces a brown discoloration of the wood, 

 which when decayed is permeated by snow-white strands of 

 mycelium that extend outwards through the bark, and give 

 origin to sporophores on the surface of the trunk. When 

 a tree is once infected the mycelium continues to extend in 

 the wood, and produces sporophores at different points each 

 season. 



Pileus corky, elastic, light, strongly hoof-shaped, 3-8 in. 

 across, very fleshy, somewhat umbonate behind, attached by 

 a narrowed portion, which sometimes is prolonged into a very 

 short stem, whitish grey or brownish, smooth, margin in- 

 curved ; flesh very thick, white ; tubes short, spores minute, 

 whitish. 



Smell acid ; epidermis thin, often cracking and peeling off 

 in flakes. Whole plant very light. 



