INJURIOUS INSECTS, FUNGOUS DISEASES, ETC. 193 



the growth of the different years. The fruiting surface 

 is white, and when bruised turns brown, and hence the 

 brackets of this species are used for sketching. 



A sap-rot fungus frequently found on city trees is Hopa- 

 lopilus gilvus (Schw.) Murrill {Polyporus gilvus Schw.). It 

 has no common name and is classed with the ordinary poly- 

 pores that live on decayed wood. 



One of the most important enemies of structural oaks and 

 chestnuts is Dmdalea quercina (Linn.) Pers. It is generally 

 found on oak and chestnut logs, ties, telegraph-poles, fences, 

 etc., all of which it destroys with rapidity. This fungus 

 also occurs on dead portions of living trees, and the sporo- 

 phores may be found growing out from large wounds. 



ROOT-ROTS 



The roots of trees are also subject to diseases of which 

 the rotting caused by the honey agaric {Armillaria mellea 

 Vahl. ) is an example. The fungus usually gains entrance 

 through some wound in the root system. The young myce- 

 lium grows into the cambium layer, attacks the living cells, 

 and finally completely encircles the base of the trunk of an 

 affected tree. The most characteristic parts of the honey 

 agaric are the hard black strands popularly known as "shoe 

 strings," which extend in all directions through the ground 

 and along the roots of affected trees. 



The danger of any root-rotting disease lies in the fact 

 that trees so affected are liable to be blown down without 

 warning. Such rots as gain entrance through]wounds at the 

 base of the trunk can be prevented by properly treating all 

 abrasions of the bark; but other forms of the disease, inclu- 

 ding the case of the honey agaric, spread through the ground 

 and are difficult to prevent. Careful inspection of such 



