FOREST PROTECTION 113 



Par, 7. Protection Against Fungi. 



The diseases of our American trees caused by fungi have been studied by 

 Dr. Hermann von Sehrenk, of the Shaw School of Botany. Still, it must 

 be admitted that our knowledge of the diseases of trees induced by cryp- 

 togamic parasites is deficient or inadequate. In the forest, obviously, the 

 present conditions confronting forestry do not allow of "tree doctoring." 

 Nurseries and young plantations in which fungi may cause enormous dam- 

 age are practically absent from our forests. Fungi directly causing the 

 death of trees, of over 12 inches d.b.h., are practically unknown. 



Saplings and poles killed by fungi die from below, whilst those killed 

 by insects die from above. 



A. Effect of Fungus Infection. 



Observations in the United States are at hand only with re- 

 ference to fungi of a technically damaging character. 



Such fungi may cause: — 



I. Disintegration of lignin, leaving the shining white 

 fibres of cellulose untouched. 



II. Disintegration of cellulose leaving a brittle brown 

 mass resembling charcoal. 



III. Disintegration of entire cell walls, leaving a hole 



or holes. 



IV. Liquification of the rosin incrustating the heart- 



wood, in which case the rosin exudes at branch 

 holes where it solidifies by oxidation, forming 

 knots, galls or streaks of rosin. 



B. Parts of Tree Infected; and Methods of Infection. 



Fungi may attack the heartwood, or the sapwood, or 

 both heartwood and sapwood. Heartwood fungi (which never 

 kill a tree directly) enter through insect mines; through axe 

 scars; through branch stubs having heartwood, or through 

 tops broken off by snow, by sleet, by falling neighbors or by 

 storm. For the latter reason, diseased timber prevails fre- 

 quently along wind swept ridges and shores, 



Sapwood fungi may use the same channels of access, or 

 may enter the wood through lightning streaks and through 

 fire clefts. Sapwood resists the attack of fungi much better 

 than heartwood as long as the tree lives. The sapwood is the 

 life zone of the tree in which it defends itself readily, by thick- 

 ening its cell walls or by cell wall incrustations, or by form- 

 ing cork against the spread of hyphse. 



In dead trees, on the other hand, sapwood decomposes 

 much more readily than heartwood owing to the absence of 



IP 



