364 



Diseases of Economic Plants 



are found in the wood. Death results either from diminu- 

 tion of water supply or from breaking of the trunk. 



Heart-rot, White wood-rot ^'^^ {Fomes everhartii (E. & G.) 

 Schr.). — This closely resembles the rot produced by 

 Fo7nes igniarius. Large, rusty-brown, woody sporophores, 



red-brown below, grow 



from wounds and 

 bear very small pores. 

 White-rot ^'^^ {Poly- 

 ponis sqiiamosus Fr.). 

 — In Europe this rot 

 affects pear, oak, elm, 

 walnut, linden, wil- 

 low, ash, birch, beech, 

 horse-chestnut, and 

 maple. In America it 

 has been reported from 

 Minnesota. The wood 

 li e c o m e s unusually 

 white and bears scat- 

 ' "' ^^Lrf .- tered series of white 



lnHHHBtt|H|Kgjg|[L The nearly circular 



^^HHHHHIPB0lli^^ bodies are 



-■B^^^^^^^^ stalked and often at- 



- ""^ ' tain a diameter of 



15 cm. When young, 

 they are soft, but 

 later become very 

 tough. The upper surface is scaly and rough. 



Sapwood rot ^^^ (Fomes fomentarius Gill.). — This rot 

 abounds throughout the northern part of the United States, 

 as one of the most common diseases of deciduous trees, 

 chiefly affecting the beech and birch. 



Decay begins in the outer sapwood and proceeds in- 

 ward. The wood is marked by irregular black lines, the 

 boundaries between diseased and normal wood. When en- 



FiG. 191. — Fomes fomentarius showing 

 hoof-shaped sporophore. After Atkin- 

 son. 



