FOMES ANNOSUS. 435 



iii. Small isolation-trenches should be dug round plants, or 

 groups of plants which have been attacked, so as to localise 

 the injury and prevent a further spread of the rhizomorphs. 

 The trenches should be far enough from the attacked plants 

 to exclude all rhizomorphs from the healthy trees. 



*2. Fames annosus, Fries. • 



a. Descriplion and Mode of A f tack. 



This parasite, formerly named Trametes radicq)erda,U. Hrtg., 



is very destructive in pine and spruce forests of North 



Germany, and is not uncommon in the British Isles ; it causes 



root-rot in the Scots pine, spruce and other conifers, and has 



Fig. 210. — Sporocarp of Fomcs annosus, Fries., on a Scots pine root. {Reduced.) 



been found on old stumps of Inrches and beech which have 

 been injured by mice, although it is probably not parasitic on 

 broadleaved species. Trees attacked by it are eventually 

 killed. Pioot rot may, however, be due to other causes. 



The infection usually comes from the diseased roots of a 

 neighbouring tree, but also from conidia. The colourless 

 soft mycelium is more delicate than that of the honey 

 fungus, resembling tissue paper, and is developed in the bast 

 and wood of the root-system of trees. The walls of the bast 

 and wood-ceils are bored and disintegrated by numerous 

 hyphae until the roots become totally rotten. The rot pro- 

 ceeds from an infected root upwards into the stem and from 

 the collar downwards into the hitherto sound roots, only in 

 the Scots pine does the resinous root-stalk form an impedi- 

 ment to the ascent of the mycelium. In spruce- wood, the 



F F 2 



