SILVER- FIR CANKER. 



451 



a case of polymorphy may be concerned here, but the 



alternate host of the fungus, if one existed, was not then 



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



infecting species of SteUaria with spores from a silver-fir 



witches - broom, and obtained Melampsorella Caryophyllace- 



(irum, Schroter, also named Melamp- 



sora Cerastii, Pers. This fungus 



attacks species of SteUaria and 



Cerastium, common weeds in fields 



and hedgerows adjoining silver-fir 



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 fulvus, Scop., 

 and Agaricus adiposus, 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 

 timber, 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. 



b. Subjects of Attack and Distribution. 



The disease is everywhere widespread in silver-fir forests, 

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



G G 2 



Fig. 220. Canker on a Silver-fir 

 about 45 years old caused by M. 

 Caryophyllacearum, Schroter. 



