71 



also upon cultural habits of those phenomena, which we have learned to 

 recognize as parasitic. 



This idea, which is also the guiding principle in the present book, has 

 led the author to undertake the first experiments for collecting the Statistics 

 of Plant Diseases. These experiments which, as already mentioned, were 

 begun with the help of the German Agricultural Society and continued by its 

 "Special Commission for Plant Protection," have now found recognition, 

 for "the "Kais. Biologische Anstalt fiir Land- und Fortswirtschaft" beginning 

 with 1905 has assumed the collection of statistics of plant diseases. 



Doubt is often expressed as to the importance of such statistics for our 

 subject and reference made to the fact that our most dangerous diseases are 

 constantly present and the statements of the statisticians concerning the 

 intensity of the attack and the amount of agricultural loss appear to 

 be influenced so individually that all certain positive figures can never 

 be attained. In opposition, it should be emphasized that I did not undertake 

 the collection of statistics in order to obtain precise figures as to the dis- 

 tribution and agricultural efifect of the different diseases. (Besides, in this 

 connection, the making of reports will gradually, with the increased educa- 

 tion of the body of observers, become as exact as it is in all provinces of 

 organic life). The chief undertaking in the collection of statistics lies in the 

 proof of the relations which the different diseases bear to climatic and soil 

 conditions felt locally or universally, as well as to cultural factors. The study 

 of the extreme forms of disease, easily verified, and the determination as to 

 which factors have produced these extreme forms makes up the productive 

 field of the statistics. 



In these studies lies the future of pathology. 



However valuable in themselves the observations as to the formal po- 

 sition and the life requirements of the parasitic micro-organisms may be, 

 nevertheless, they form only one link in the chain of investigations and be- 

 come important only in the determination of their relation in nature and in 

 tJie usual practice of agriculture. And this we can recognize by means of a 

 carefully arranged statistical office showing the conditions governing the in- 

 crease or decrease of diseases. 



This knowledge leads to the prevention of diseases by means of an ever- 

 developing plant hygiene and plant pathology must develop further in this 

 direction in the future. 



