PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 323 



of citizens are interested, while 600 or 700 plant diseases are 

 known at present, half of which have been studied carefully. 

 In the same time, papers on plant pathology have multiplied until 

 6, GOO or 7,000 have appeared in the United States. 



In the early days of plant ])athology, a considerable numl)er 

 of botanists gave attention to abnormal morphology, while certain 

 mycologists were directing their efforts toward causal organisms. 

 The greatest advance has been in bacteriological plant pathology, 

 based on the bacteriological methods of animal pathology. 

 Fungal plant pathology has followed, while the physiological 

 aspect is only beginning to attract attention. 



It is now recognized that plant diseases may be caused by 

 conditions of environment as well as by parasitic organisms. 

 Even when a causal organism is present, its effects are usually- 

 made possible or more dangerous by some unfavorable condition, 

 as lack of sufficient nourishment, over nourishment, error in 

 cultivation, improper water relations, bad soil conditions, or lack 

 of aeration of the soil. Recognition of the fact that any one of 

 these factors may induce plant disease, or may so weaken the 

 hosts that they fall prey to ])arasites has in the last decade or two. 

 greatly enlarged the scope of plant pathology. It is now known 

 that a plant immune in one environment may not be in another, 

 and that a plant may be immune on a certain soil one year and 

 not the next. This points to a ])hysiological relationship, through 

 which the vigor and the resistance of the plant varies from time 

 to time. In short, jilant ]iathology has, in recent years, passed 

 from the almost exclusive consideration of causal organisms and 

 their effects to a vastly broader and more promising basis. 



Conditions produced by insects or other animal organisms 

 are diseases when they result in tissue changes, quite as much 

 as are plum-pockets, club-root, crown-gall, and other hypertro- 

 phied conditions caused by fungi or bacteria. Why hypertrophy 

 of host tissues results in some instances, or prolonged life results 

 in one case and early death in another, remains to be thoroughly 

 investigated. These are considerations for the plant pathologist, 

 whatever the nature of the causal organism. 



Necessarily, remedial measures received early attention from 



