PINE ROOT-FUNGUS. 249 



the roots of a healthy tree. The roots then die, the diseased wood turns 

 violet and pale brown -yellow with black spots surrounded with a white 

 zone, then hollows become excavated, and the whole rots. But infection 

 can also be conveyed to wound-surfaces on the roots of healthy trees by 

 mice, insects, &c. The soft, transparent, or snow-white mycelium develops 

 beneath the bark and permeates the cambium and the woody tissue of 

 the roots and the butt of the tree, the cell-walls being destroyed by masses 

 of mycelial filaments. This rottenness soon spreads up into the stem by 

 the cambium and the medullary rays except in the Scots Pine, in which 

 morbid resinification confines the rot to the butt. Destroying the living 

 cells as it spreads, the mycelium soon penetrates the wood of the roots 

 and extends more slowly into the bark, where it forms long thin tissue- 

 paper-like strands, with small yellowish- white pustules protruding between 



Fig. 67. 



Half natural size. 

 Sporophore of Fomes annosus on Scots Pine root. 



bark-scales, these being a sign that the disease has complete hold of the 

 tree. The mycelium can now spread and carry infection to neighbouring 

 plants or trees. Small, glossy, yellowish-white, grape-like masses of 

 sporophores appear mainly on the roots or at base of stem between 

 the bark-scales, and form thin concave woody chocolate-brown cushions, 

 snow-white below, which unite with similar adjoining groups as flat in- 

 crustations or bracket-shaped excrescences up to a foot broad. But 

 mould-like masses of conidia are also produced where the mycelium comes 

 out into free air. 



Remedy. Direct spore-infection can hardly be prevented; but when 

 the disease has broken out, the diseased plants should be grubbed up and 

 the infected parts burned before the sporophores ripen, and broad-leaved 

 trees planted in place of the Conifers lifted. Infected patches isolated 

 by narrow trenches usually produce sporophores on the roots cut through, 



