FIR DISEASES 171 



ing root-rots of various conifers and hardwood trees but have 

 never been accurately studied. 



Symptoms. 



Lateral roots are attacked even to considerable depths in the 

 soil. The mycelium from the point of infection spreads out 

 in the cambium and bark in yellowish fan-like plates. The 

 root is girdled and killed. The mycelium then penetrates the 

 sapwood, destroying first the medullary-rays. The affected 

 region is bordered by a reddish zone and at times by a jet- 

 black line. The heartwood at first is not penetrated because of 

 its highresin-content. Certain areas of heartwood are attacked, 

 however, and long pits formed by the complete destruction 

 of the tissues. At other times the inner layers of heartwood 

 may be largely destroyed, leaving a resinous layer of unaffected 

 wood between the decayed region and the sapwood. The 

 decayed heartwood is brownish or yellowish. Numerous 

 delicate brown strands of mycelium penetrate the wood where 

 openings have been formed. The cambium region is replaced 

 by a thick felt of mycelium. 



The fruitiiig-bodies of the causal fungus are formed on the 

 surface of the ground. A long, fleshy, tuber-like body at- 

 tached to the diseased root pushes upward through the soil and 

 bears the upright fruiting-body on its tip. This fruiting-body 

 is a large, fleshy, compact, whitish, much branched structure, 

 often as much as ten inches across and equally as high. The 

 branches terminate as thin leaf-like but much crumpled plates 

 which stand upright or horizontally. The perennial tuber- 

 like attachment to the roots is often fifteen or more inches 

 long and a new fruiting-body is formed from its tip each year. 



Cause. 



The yellow root-rot of conifers is caused by the fungus 

 Sparassis radicata of the family Clavariacese. The spores are 



