CHAPTER III 

 BODY AND BRANCH DISEASES AND INJURIES 



Many diseases and injuries of the bark and wood 

 are more or less common to all kinds of trees. Extremes 

 of temperature, lightning, mistletoes, lichens and some species 

 of fungi are some of the causal agents which affect trees in 

 general. As in the case of the diseases and injuries common 

 to the seedlings and leaves of many kinds of trees, the primary 

 causal agents of the diseases affecting bark and wood are often 

 difBcult to determine. It is only by a careful analysis of the 

 conditions siu-rounding the tree in question and by close ob- 

 servation of other trees in the vicinity that clues can be ob- 

 tained. Also, in such cases, the knowledge of similar tree 

 troubles may be essential in determining the exact cause. 

 Many of the diseases and injuries of the branches and trunk 

 affect the appearance of the leaves before direct attention is 

 called to the primary injury. 



In general, the presence or absence of fruiting-bodies 

 of fungi on the bark is of but little value in determining 

 whether or not the trouble is caused by a specific fungus. 

 This is due to the fact that numerous species of fungi 

 find excellent conditions for growth in dead bark and some 

 species follow very closely any injuries to the bark. A 

 trained pathologist must be closely observant to assert even 

 tentatively that a fungus found on dead areas of bark is 

 responsible for the lesion. The only sure way of proving 

 the fungus to be the cause of disease is the usual procedure of 

 isolating and growing the fungus in pure cultures and inoculat- 



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