Introduction, 



The diseases of plants and their causes may be grouped as 

 follows : 



Organic diseases, i. e., those caused by living organisms 

 such as : 



Fungi. 



Bacteria. 



Slime molds. 



Flowering plants. 



Insects and other animals. 

 Inorganic diseases, i. e., those due to other causes than living 

 organisms : 



Unfavorable conditions of soil, etc. 



Unfavorable conditions of weather, etc. 

 It is not the purpose of this work to consider all of the dis- 

 eases of Minnesota plants. The attack of insects furnishes a 

 vast field of research which is best left to the entomologist. By 

 far the most widely distributed and most destructive of Minne- 

 sota plant diseases are organisms belonging to the plants known 

 as fungi. Bacteria are responsible for a considerable number 

 and the fungus-like animals, known as slime-molds, are respon- 

 sible for a few. In addition the flowering plants cause several 

 diseases. There are also to be considered those diseases which 

 are caused by inorganic agencies as drought, heat, wind, hail, 

 lightning, frost-cracks, sunscalds, etc. This work will not ad- 

 mit of a discussion of the latter group. 



It is well at the outset to note that disease cannot be easily 

 defined. One might consider any variation due to the derange- 

 ment from the most favorable conditions of the life of a plant 

 as a disease. The most favorable conditions in all respects are 

 seldom, if ever, realized. When the favorable conditions of life 

 are so seriously interfered with by any agency, so that the life 



