DISEASES OF SHADE AND FOREST TREES. 



95 



1. DISEASES OF THE FOLIAGE. 



The foliage contains the greater amount of the green color- 

 ing matter, or chlorophyll, by which a plant is enabled to 

 utilize the raw food materials which it receives from the air 

 and soil. Therefore any great reduction of the foliage sur- 

 face during the growing season results in a proportional 

 reduction in the working power of the plant and also mars 

 its beauty for ornamental purposes. 



Fig. 36. Chestnut Leaf Spot. (From Report of X. J. Experiment 

 Station, 1896, Fig. 59.) 



LEAF SPOTS. 



I In >e diseases are caused by a number of parasitic organ- 

 m<. principally fungi and bacteria, which cause discolored 

 a- <ai the foliage, frequently followed by a breaking out 

 the dead tissues, thus leaving unsightly holes. The char- 

 ter and severity of these various leaf spots vary with the 

 lisms to which they are due and also with climatic con- 

 litions. Among the most important of these leaf-spot fungi 

 shade trees are the following : 



