142 ILLINOIS STATE ACADEMY OF SCIENCE 



lettuce or radish bed in the city garden, while much effort 

 would be expended justifiably upon the group of diseases 

 attacking more important crops such as corn, cereals, 

 and fruits. 



Diseases unimportant economically need to receive a 

 reasonable amount of study because their study may lead 

 to the development of facts applicable in an important 

 way to the understanding of those diseases which are 

 economically important. Such study also serves directly 

 in the advancement of purely scientific knowledge which 

 is, of course, the basis of all of our practical applications. 

 In this category will be included all diseases occurring on 

 all plants whether weeds, herbs, shrubs or trees, not us- 

 ually grown as crops. 



The scope of the survey must lie largely, if not entirely, 

 within that group of disease caused by microscopic fungi 

 and organisms of an allied nature. This is especially true 

 since diseases of this type of origin constitute by far the 

 greater number and variety of affectations to be dealt 

 with among plants, and because those morbid conditions 

 due to the attack of predatory insects have long since 

 been recognized as lying within the province of the ento- 

 mologist. 



THE STUDY OF DISEASE DISTRIBUTION 



In its essential aspect, this phase of the survey work 

 may be expressed briefly as determining in what localities 

 diseases occur. In the practical application of control 

 measures, as well as in the purely scientific consideration 

 of plant diseases, a knowledge of geographic distribution 

 is often of real value. In the application of control 

 measures it may indicate to what extent the program is 

 practical, or it may serve to determine the amount of 

 territory to be included in the program. And in course 

 of time it may serve to determine the degree of effective- 

 ness which the control measure has attained. From a 

 scientific view point, information of real value may be 

 developed through the correlation of details of time, place 

 and severity of infection with weather conditions, edaphic 

 host relations, etc. The ultimate scientific use of these 

 facts would be in the development of principles of an 



