CHAPTER IV. 



PLANT DISEASES AND INSECTS. 



/. Vegetable Pathology. 



The subject of vegetable pathology is yet so new that the 

 term itself is unfamiliar. It has long been known that plants 

 have diseases, but in a popular and practical way the knowl- 

 edge has been productive of few results until the present time. 

 In general, the most destructive diseases are those caused 

 by the attacks of parasitic plants, yet there are diseases of 

 nutrition. The term vegetable pathology has come by cus- 

 tom to apply only to diseases which are fungous or fungoid 

 in their nature, a limitation which in many respects is unfortu- 

 nate. 



Great activity has been shown in the study of injurious 

 fungi in very recent years, and results of inestimable economic 

 value have been obtained. The investigation has been un- 

 dertaken by specialists connected with the agricultural col- 

 leges, and later by those working with the experiment stations, 

 but the work fostered by the Department of Agriculture has 

 been the most systematic and various. The section of vege- 

 table pathology has a considerable force of skilled men in the 

 laboratory and field. During 1889 agents of the section were 

 located in New Jersey, Delaware, Virginia, South Carolina, 

 Mississippi, Missouri, Michigan, Wisconsin and California. 



A great range of subjects has been investigated, and the 

 literature of plant diseases is increasing with great rapidity. 

 The most signal advantages of these investigations have 

 been those in connection with the diseases of grapes. 

 The black-rot and mildews have been so disastrous to 

 grape culture in many parts of the country that growers 



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