186 SHADE-TREES IN TOWNS AND CITIES 



those of the former. The caterpillars bore near the surface 

 and are easily dug out and destroyed. Where the insects 

 are observed in great numbers it will pay to whitewash the 

 trunks several times during the season. This will repel the 

 moths that would otherwise deposit on the trunks, and it 

 would cover over or partly fill the small holes that have 

 been made by the insects. 



Bark Borers. Some borers which attack trees work in 

 the cambium layer just under the bark, making a series of 

 galleries which interlace each other and extend all the way 

 around the branches of infected trees. 



The effect of these borings is slow girdling. The circu- 

 lation of sap is cut off and the upper part of the branches 

 die. 



Some of the more common bark borers attacking shade 

 and ornamental trees are the bronze birch borer (Agrilus 

 anxius Gory. ) , which attacks the various species of birch, 

 the two-lined chestnut borer {Agrilus bilineatus Weber), 

 which infests the chestnut and the oak, and the hickory- 

 bark borer {Scolytus quadrispinosus Say), which is most 

 injurious to the hickory. 



The cutting out of infested branches sometimes checks 

 the disease if it has not spread far down to the trunk. In 

 the majority of cases, however, there is no remedy for trees 

 once attacked by these borers. 



FUNGOUS DISEASES 



Many diseases of trees are caused by low forms of vege- 

 table life, known as fungi, which live upon and within the 

 tissues of the higher plants. They possess none of the green 

 coloring matter of ordinary vegetation and are made depend- 

 ent upon the organic matter prepared by green plants. They 



