SILVER- FIR CANKER. 



451 



a case of polymorphy may be concerned here, but the 



aUernate host of tlie fungus, if one existed, was not then 



known. In 1901, however, E. Fischer, of Berne, succeeded in 



infecting species of Stdlaiia with spores from a silver-fir 



witches - broom, and obtained Melampsorella Caryophyllace- 



firiiin, Schroter,also nsuned Mdamp- 



sora Cerastii, Pers. This fungus 



attacks species of Stdhiria and 



Ccmstium, common weeds in fiekls 



and hedgerows adjoining silver-lir 



forests. 



The damage done is direct and 

 indirect, the former consisting in 

 loss of increment and depreciation 

 of the quality of the wood, as 

 cankered wood cannot be used for 

 constructions. The indirect damage 

 consists in increased danger of 

 breakage by storms or snow, and 

 a greater disposition to insect 

 attacks and those of other fungi, 

 such as Polyporus fidvus, Scop., 

 and Agaricus adiposiis, Fr., which 

 soon render the wood very brittle. 

 A practical distinction is made be- 

 tween sound and diseased cankers ; 



sound cankerous wood is 30 per cent, heavier than uncankered 

 wood, it is also harder, less fissile, and absorbs only half as 

 much water. Sound cankerous trees yield some pieces of good 

 limber, but badly cankered trees are only fit for fuel. 



Several cankers may be sometimes seen on the same tree, 

 and cankered trees may die outright in hot summers. The 

 canker may live for 50 years and longer. Mr. H. Ingold has 

 calculated, that, in the Vosges, 21 cankered trees are broken, 

 to one sound tree, and 11 dry up, to one sound tree. 



Fig. 220. — Canker on a Silver-fir 

 abfjut 4 years old caused by M. 

 C'(i)i/ophi/llitct(inini,iit;hT'uteT. 



b. Suhjeds of At lade and Distributiun. 

 The disease is everywhere widespread in silver-fir forests, 

 both mixed and pure, and especially in the Black Forest, 



G G 2 



