SIGNPOSTS ALONG THE PHYTOPATHOLOG1CAL PATH 419 



Schroder and Dusch; and (3) the establishment of pathogenicity 

 by compliance with axiomatic rules of proof, called Koch's rules. 

 Gradually other techniques from procedures developed in bac- 

 teriology were adapted for use in studying fungi. These tech- 

 niques involve the influence of such environmental factors as tem- 

 perature, food requirements, and hydrogen-ion concentration of 

 the medium and the complex reactions involved in studies of 

 antigenic properties of fungi. 



SIGNPOSTS ALONG THE PHYTOPATHOLOGICAL PATH 



Certain outstanding events and discoveries indicate the course 

 of development in any field of science. Those in phytopathology, 

 as has been stated, have been very directly and quite uniformly 

 related to mycology. The most significant are categorically listed 

 as follows: 



1. The epiphytotics of late blight of potatoes in 1843, 1844, 

 and 1845 in northern Europe and the British Isles. The destruc- 

 tion of the potato crop was so complete that in Ireland alone 

 approximately a quarter of a million persons died of famine. As 

 a secondary consequence of the catastrophe, attempts were made 

 to determine the cause and control of this potato disease, and 

 plant pathology, as a science, may properly be concluded to have 

 originated with these studies. For the first time the public appre- 

 ciated the significance and the necessity of plant pathological 

 investigations. 



2. The publication in 1853 of the first textbook of plant 

 pathology by Julius Kiihn, who is generally regarded as the 

 father of plant pathology. In this book considerable emphasis 

 is placed on the disease itself rather than on its cause. This is 

 true also of important books that followed, such as those by 

 Berkeley, Cooke, Hartig, Sorauer, W. G. Smith, Tubeuf, Kirch- 

 ner, Ward, Comes, Prillieux, Massee, and Viala; all of these, how- 

 ever, are preponderantly mycologic. 



3. The establishment of proof of the heteroecism of rusts by 

 de Bary in 1864 to 1865. The relationship between rust on wheat 

 and that on barberry had long been suspected by farmers. In 

 fact, they had compelled the enactment of legislation providing 

 for the eradication of barberry as early as 1660 in France and as 

 early as 1726 in the state of Connecticut. 



