3IO 



GENERAL PLANT PATHOLOGY 



sitica, a single downy woodpecker carrying 757,o74 spores.^ Wood- 

 boring insects (Family Scolytid^) of the genera Dendroctonus, 

 Scolytus, Tomicus are responsible agents in the destruction of trees 

 opening up holes through which fungi may .gain entrance. Horses 

 do considerable damage to trees by stripping off the bark with their 



teeth, and street trees cannot be too 

 soon or too carefully protected from 

 such ravages, for a tulip tree planted in 

 the afternoon in front of the house of 

 the writer in West Philadelphia had a 

 strip of its bark removed by the curb- 

 stone horse of a deUvery wagon before 

 nightfall of the same day (Fig. 124). 



Telegraph wires stretched in every 

 direction rub against the trunks and 

 limbs of trees, and do mechanic injury 

 in this way, but, if the insulation is 

 rubbed off the tree may be badly burned, 

 or even set on fire by the electric cur- 

 rent, especially on rainy days when 

 there is a direct grounding of the cvu:- 

 rent through the water running down 

 the crevices of the bark. Many trees 

 in our cities are planted too close to the 

 curb and the wheels of passing wagons 

 tear off pieces of bark (Fig. 141). 

 Farmers in plowing, hoeing, mowing 

 and cultivating the soil injure the 

 roots and stems of cultivated plants 

 and open the way for the entrance of destructive fungi. The blazing 

 of trees by surveyors, the careless system of lumbering, careless trans- 

 planting of young trees, are fruitful sources of injmy to trees. Careless 

 pruning (Figs. 125 and 126) of trees by inexperienced men, such as was 

 prevalent in Philadelphia before the Park Commission undertook to 

 properly care for the trees, caused the death of many fine shade trees. 



Fig. 125. — Decay following un- 

 skillful pruning. (Sturgis, W. C, 

 Rep. Conn. Agric. Exper. Siat., pi. 

 Hi, 1900.) 



• Heald, F. D. and Studhalter, R. A.. Preliminary Note on Birds as Carriers 

 of the Chestnut Blight Fungus. Science, new ser., xxxviii: 2^8-280, Aur. 22, 1913. 



