BIRCH POLYPORUS 191 



white strands of mycelium. The Uber and bark are also 

 attacked, and the fruit of the fungus first appears under 

 the form of small white knobs in cracks of the bark, each 

 knob developing into a pileus or spore-producing structure. 

 Although the pileus is an annual production, it is probable 

 that the mycelium is perennial in the wood, gradually 

 encroaching on sound portions of the trunk, and producing 

 new pilei every season. 



Preventive Means. — Healthy trees are first inoculated 

 at some broken surface by means of floating spores; hence, 

 to prevent the diffusion of spores, the fungi must be 

 systematically destroyed. An old birch-tree having the 

 trunk ornamented with numerous well-developed pilei of 

 Polyporiis beiulinus is certainly an artistic object, and 

 numerous such can be seen in the woods at Birklands, in 

 Sherwood Forest ; but where the trees are grown for other 

 purposes, such diseased examples should be promptly 

 removed, otherwise they form a centre from which myriads 

 of spores are being liberated annually, and the spread of 

 the disease under such favourable circumstances is certain. 



Prillieux, Mahid. des Plantes Agric.^ vol. i. p. 367. 



HEART- WOOD ROT 



{Polyporus hispidus, Fries.) 



This fungus attacks the majority of broad-leaved trees ; 

 in orchards the apple is most frequently attacked. The 

 parasite is readily recognised by its coarsely velvety, dark 

 brown pileus or upper surface, thick, dark-coloured, fibrous 

 flesh, and long, yellowish-brown pores. Large specimens 



