54 



A TEXT-BOOK OF BOTANY. 



Chestnut Bark Disease is caused by a fungus parasite known 

 as Diaporthe parasitica Murrill, and is said to very closely re- 

 semble the parasite found in Italy, EndotJiia radicalis. This 

 fungus has been the cause of very great destruction of chestnut 

 trees in the eastern United States. When any of the spores of 

 this fungus gain entrance into a wound on any part of the tree, 

 thread-like mycelia are developed in the inner layers of the bark, 

 and these spread concentrically until they girdle the trunk or 



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Fig. 30. Large Chestnut tree partly killed by the bark disease. Note branches 

 in the center either killed or bearing dwarfed leaves, and the other larger branches still 

 unaffected. — From photograph by Haven Metcalf. 



limb, so that if it happens that the trunk is affected the entire tree 

 may die within the year, while if it is the smaller branches which 

 are attacked, only those parts beyond the point of infection are 

 killed, while the remainder of the tree will survive for some 

 years (Fig. 30). 



When the bark is attacked by the fungus it shows minute, more 

 or less crater-like spots of a yellowish-orange or reddish-brown 



