14 DISEASES OF DECIDUOUS FOREST TREES. 



branches, which make possible the entrance of disease-producing 

 organisms at a later date. The winter of 1904-5 was characterized 

 by extreme cold and resulted in considerable destruction to forest 

 trees all over the country. Hail, sleet, and snow produce injuries to 

 forest trees which are often extreme ; their chief importance lies in the 

 fact that they produce injuries leading to diseases caused by fungi or 

 insects acting upon such trees at a subsequent date. 



INJURIES CAUSED BY ANIMALS, WIND, ETC. 



The injuries caused by the biting or chewing of animals may be 

 classed in the same category as the injuries referred to under snow 

 and ice, and injuries produced by windstorms may also be placed in 

 the same class. It is very rare to find a large forest tree which is 

 seriously affected because of such injuries, except in the case of vio- 

 lent windstorms. The chief importance of such wounds lies in the 

 fact that they open up pathways for destructive forms of insects or 

 fungi, which are referred to more in detail hereafter. Of these fac- 

 tors, the action of the wind in breaking off branches from more or 

 less mature trees must be considered as the most important. 



DISEASES CAUSED BY MISCELLANEOUS PARASITIC AND SAPRO- 

 PHYTIC ORGANISMS. 



The diseases caused by parasitic or saprophytic organisms may for 

 convenience be divided into three groups: Those caused by insects, 

 those caused by parasitic higher plants, and those caused by fungi 

 and bacteria. 



DISEASES CAUSED BY INSECTS. 



The disturbances in the activities of the living parts of trees caused 

 by insects are not usually classed in any discussion on diseases of 

 plants, although the changes which they produce undoubtedly should 

 be considered rather from the standpoint of the plant than from that 

 of the insect causing them. No special reference will be made in 

 this discussion to any of the diseases of broadleaf trees caused by 

 insects. These have been described in the publications of the Bureau 

 of Entomology of the United States Department of Agriculture by 

 Dr. A. D. Hopkins (42, 43), and a number of them by Dr. E. P. 

 Felt (18 to 21) and others (22, 49, 66, 67, 87) are mentioned in the 

 bibliography. 



DISEASES CAUSED BY PARASITIC HIGHER PLANTS. 



Many species of deciduous trees are attacked by the common mis- 

 tletoe (Phoradendron jlavescens (Pursh) Nutt.). This parasite is very 

 prevalent from the vicinity of the Ohio River southward, and west- 



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