414 DISEASES OF ECONOMIC PLANTS 



Prominent among the rots are these following: — 



Heart rot (Trametes pini (Brot.) Fr.). — In the North 

 this rot affects all conifers, invading first the heartwood, 

 very rarely the sap wood. The wood is not wholly destroyed 

 by the fungus ; but series of small holes with silvery lin- 

 ing are noted in early stages. In spruce the color of the 

 wood itself is changed to a light purplish gray, later to a 

 reddish brown netted with small black lines. Small patches 

 of white follow, which later develop into holes, arranged in 

 series to correspond 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 whole wood mass to 

 mere fiber. 



The sporophores may consist of either 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. 



"White heart rot {Fomes igniarius (L.) Fr.). — This is 

 the most important and widespread of the heart rots, 

 and the 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, 

 willow, mountain maple, hornbeam, white elm, sugar maple, 

 red maple, silver maple, striped maple, yellow birch, butter- 

 nut, black walnut, oaks, apple, and hickory. The amount 

 of damage done by it is beyond estimation. In many 

 cases almost the entire timber stand is ruined. Actual 

 count has shown 90 to 95 per cent of otherwise market- 

 able trees valueless. 



