1 9 1 7] STE YENS— P LA NT PA T HO LOG Y 2 99 







agents, but it really was a rigid, scientific method which gave us our 

 present knowledge of these diseases. The valuable results of the 

 work on cereal smut infection furnish a fine example of achievement 

 in disease-prevention that could not have been attained without 

 both basic knowledge in mycology and a technique enabling 

 trustworthy experimentation. 



Upon entering a new biological territory, the first work is to 

 collect and to classify, to know the material. So in the new field 

 of plant pathology much of the early work was descriptive. 

 The number of important plant diseases that are reasonably 

 well described in two volumes of the Report of the United 

 States Department of Agriculture for the years 1887 and 1888 is 

 remarkable. 



While the descriptive period in plant pathology is not entirely 

 past, trivial diseases of cultivated plants, weeds, and wild plants 

 still remaining undescribed, there have been very few really impor- 

 tant diseases of general interest recently discovered in this country, 

 few which compare in importance with the apple bitter rot, tomato 

 leaf spot, onion smut, potato blight and scab, the cereal rusts or 

 smuts. Many of the diseases recently described are of minor 

 importance or are at present of very narrow geographic range; 

 some have never been noted except by those who described them. 



With the general principles of treatment established and the 

 field for discovery of new diseases dwindling in importance, the 

 time has now come when further progress, with rare exception, 

 must be the outcome of fundamental, special knowledge and crucial 

 experiments. It is evident that the easy crop from the virgin 

 soil has been harvested, and that now we are entering upon the era 

 of intensive cultivation. 



The conquests of the future will be mainly the result of intensive 

 study of the diseases and disease agents now known. Compare 

 the degree of thoroughness of our knowledge of any one plant 

 disease with any one disease in medicine. For example, compare 

 from the research viewpoint our knowledge of Pseiidomonas 

 campestris with that of Bacillus typ hosts; of the morbid histology 

 of wheat rust with that of diphtheria; of the "epidemiology" of 

 any plant disease with that of any human disease. Of course, the 



