398 DISEASES OF CULTIVATED PLANTS 



the fungus also grows on fallen wood, all such should be 

 removed. 



Hartig, Zersetz. des Holzes, p. 103. 



Prillieux, Malad. des Plantes Agn'c, i, p. 307 (1897). 



Oak canker. Professor Potter has indicated a canker of 

 the oak, caused by Ste renin quercinum (Potter). The fungus 

 appears to be a wound-parasite, and causes a canker by the 

 destruction of the cambium year by year, by which the forma- 

 tion of wood and bast is prevented, the result being a canker- 

 like wound, surrounded by a rugged wall of callus surrounding 

 a wound that never heals up. The parasite is most active 

 during the winter, and destroys the cambium and wood 

 formed during the summer. The entrance of the parasite is 

 usually effected around the insertion of a dead branch. A 

 series of cultures, extending over several years, clearly proved 

 that the fungus first observed on cankered spots was the 

 primary cause of the disease. 



The action of the parasite on the wood is specially notice- 

 able in the brown discoloration of the medullary rays. The 

 appearance of ' partridge wood,' characteristic of the action of 

 Stereum frustulosum, is not produced by 5. quercinum. 



Sporophore resupinate, with slightly raised edge, pale grey 

 to pale brown, often with a lighter margin, |-f in. across, only 

 two hymenial layers present in old specimens, hasidia smooth ; 

 spores elliptical, 8-5 x 4*3 /*. 



Potter, Trans. Engl. Arbor. Soc. t p. 105 (1901-02). 



Stereum rugosum (Fries.), although often living as a sapro- 

 phyte, can also live as a parasite, and is especially destructive 

 to the cherry-laurel, which in some districts cannot be grown 

 on account of this pest. The cherry-laurels in the Queens' 

 Cottage Grounds, Kew Gardens, are much injured. 



Broadly effused, sometimes shortly reflexed, coriaceous, then 

 rigid, pale greyish-yellow, changing to red when bruised or 

 scratched ; spores elliptical, 1112x45/'. 



CLAVARIACEAE 



A primitive type of the Basidiomycetes. In the simpler 

 forms consisting of a simple, erect, club-shaped body, covered 

 everywhere with the hymenium ; in the higher forms the 



