TREE DISEASES 153 



STUDY II. TREE DISEASES 



Becavise trees have wants analogous to those of human 

 beings, they also have diseases similar to those which 

 afflict human beings. In many cases these diseases act 

 like cancerous growths upon the human body; in some 

 instances the ailment may be a general failing due to im- 

 proper feeding, and in other cases it may be due to inter- 

 ference with the life processes of the tree. 



How to tell an ailing tree: Whatever the cause, an 

 ailing tree Avill manifest its ailment by one or more symptoms. 



A change of color in the leaves at a time when they should 

 be perfectly green indicates that the tree is not growing 

 under normal conditions, possibly because of an insufficiency 

 of moisture or light or an overdose of foreign gases or salts. 

 Withering of the leaves is another sign of irregularity in 

 water supply. Dead tops point to some difficulty in the 

 soil conditions or to some disease of the roots or branches. 

 Spotted leaves and mushroom-like growths or brackets 

 protruding from the bark as in Fig. 108, are sure signs of 

 disease. 



In attempting to find out whether a tree is healthy or 

 not, one would therefore do well to consider whether the 

 conditions under which it is growing are normal or not; 

 whether the tree is suitable for the location; whether the 

 soil is too dry or too wet; whether the roots are deprived 

 of their necessary water and air by an impenetrable cover 

 of concrete or soil; whether the soil is well drained and 

 free from foreign gases and salts; whether the tree is receiving 

 plenty of light or is too much exposed; and whether it is 

 free from insects and fungi. 



If, after a thorough examination, it is found that the 



