60 MANUAL OF TREE DISEASES 



tips of the affected branches may be pruned off, thus removing 

 permanently the infected parts of the tree. However, if the 

 tree is badly infested and new plants persist in appearing, 

 this procedure results in excessive pruning and a deformed 

 tree. It is said that the parasites may be successfully eliminated 

 by the first method and the tree left to its natural form of 

 growth if proper and constant attention is given to the work. 



In the forest where these pests often occur on twenty-five to 

 fifty per cent of the stand of .conifers, it is essential that forest 

 management plans should incorporate the elimination of all 

 affected trees during lumbering operations. Seed trees which 

 are left should be chosen with regard to their freedom from 

 mistletoe. 



References 



Bray, W. L. The mistletoe pest in the southwest. U. S. Dept. Agr. 



Bur. PL Ind. Bui. 166 : 1-39, pis. 1 and 2, figs. 1-7. 1910. 

 Weir, J. R. Mistletoe injury to conifers in the northwest. U. S. 



Dept. Agr. Bui. 360 : 1-39, pis. 1^, figs. 1-27. 1916. 

 Weir, J. R. Larch mistletoe: some economie considerations of its 



injurious effects. U. S. Dept. Agr. Bui. 317 : 1-25, figs. 1-13. 



1916. 

 Hedgcock, G. G. Notes on some diseases of trees in our national 



forests. V. Phytopathology 6 : 175-181. 1915. 

 Hartig, R. Phanerogams. In Text-book of the diseases of trees, 



pp. 23-34, figs. 1-7. 1894. 

 Trelease, W. The genus Phoradendron, pp. 1-224, pis. 1-245. Univ. 

 of lU. 1916. 



Electrical Injuries 

 Caused by current electricity and lightning 



Trees may be more or less seriously injured by contact with 

 service wires carrying current electricity and by strokes of 

 lightning. In both types of injury the actual killing of the 

 living tissues of the tree is due to the production of heat when 

 the current meets with the high resistance of the tissues. Much 

 of the damage often ascribed to overhead wires is not so much 



