Trees and Timber 359 



spond with the annual rings, and as the disease progresses 

 result in a series of vacant spaces separated only by plates. 

 In tamarack the decay finally destroys the plates, reducing 

 the v.'hGle wood mass to mere fiber. 



The sporophores may consist either of brackets or of 

 extended sheets with shallow, pit-like pores on the under 

 side. They are cinnamon-brown on the lower surface and 

 much fissured and broken on the black, charcoal-like upper 

 surface. Prevention is best effected by proper thinning, 

 removing diseased trees, and destroying fruiting bodies. 



White heart-rot''^'-' {Fomes igniarius Gill.). — ^ This is the 

 most important and widespread of the heart-rots, and one 

 which has the widest range of host plants. It is known in 

 Alaska, Canada, the United States, and in South America to 

 Patagonia, growing upon beech, aspen, birch, poplar, willow, 

 mountain maple, sugar maple, hornbeam, white elm, butter- 

 nut, black walnut, oaks, and hickory. It is common on fruit 

 trees, especially when near forests. The amount of damage 

 done by it is beyond estimation. In many cases almost the 

 entire timber stand is ruined. Actual count has shown from 

 90 to 95 per cent of otherwise marketable trees valueless. 



Heart-rot, while chiefly of the heartwood, may, when 

 started, encroach upon the sapwood, even to the youngest 

 layers, and death may result by weakening the tree to the 

 breaking point. The causal fungus enters through wounds, 

 particularly broken stubs, and usually produces its sporo- 

 phores at these points after the rot has extended a meter or so 

 in both directions from the infection point. The first sure 

 external sign of the disease is the presence of the sporophores, 

 although sounding with the ax may sometimes be relied upon. 



The sporophores, numbering sometimes as many as 

 twelve on a tree, are shelving, hoof-shaped bodies from 

 25 to 30 cm. wide. The upper surface is brown, in later 

 stages black, hard, smooth, concentrically marked with 

 age, finally seamed and cracked. The pores are in layers, 

 approximately annual, and the lower surface is gray to red- 

 brown. 



