62 



tions and by the distribution of popular treatises. More detailed references 

 to zoological literature are to be found in the third volume of this manual. 



The number of text-books and manuals of phytopatholoj^' has grad- 

 ually been increased since the publication of Kiihn's "Krankheiten der Kul- 

 turgewachse," as the understanding of the national economic significance of 

 phytopathology has increased. First of all comes Orstedt's "Om Sygdomme 

 hos Planterne, som foraarsages af Snylteswampe, navnlig om Rust og 

 Brand," Kjobenhavn 1863. This work was followed in 1865 by later reports 

 on the alternation of hosts by rust fungi (Gymnosporangium Sahinae). 

 About this time Hallier's^ book appeared which must be given more 

 especial attention in a history of plant diseases because of the author's stand- 

 point. Hallier's views leading to sharp literary disagreements, especially 

 with de Bary, may be found in extenso in his later writings'-. In his 

 "Festkrankheiten der Kulturgewachse," he gives a list of investigations on 

 the Peronosporeae and believes he has permanently established by these 

 the correctness of his "Plastidcn Theory." At the time of tiie "Cholera 

 meeting" in Weimar (1868), Hallier first made the assertion that the forms, 

 summarized as Fission fungi (Schizomycctcs) by Nageii were not indepen- 

 dent organisms, but represent the products of the plasma of different groups 

 of filament fungi. Hence Nageli's family of the Fission fungi should be 

 stricken out of the classification and infectious diseases as a whole be traced 

 back to the action of such plasma-products ("Plastiden"). "In order there- 

 fore to discover the origin of infectious diseases, it is necessary in every case 

 to ascertain by investigation which definite fungus produces the cells of con- 

 tagion from its plasma (bacteria, micrococcus etc.) and in what way this 

 takes place." In regard to the potato disease produced by Phytophthora, he 

 does not question whether this fungus is the cause of the disease, but only 

 whether it may cause it less directly than would bacteria. "I have proved 

 first and foremost that the bacteria which are the absolute cause of the pota- 

 to pest, are produced by the "Plastiden" of the Phytophthora and that these, 

 when once formed, are absolutely equal to the production of the plague; that 

 there is no further need of the mycelium and buds of the Phytophthora." 

 His numerous experiments ultimately led him to the view that, in all in- 

 fectious diseases, human, animal and vegetable, three main points undoubted- 

 ly come under consideration: (i) The absolute cause; (2) External or 

 general furtherance (chance causes or predisposition) ; ('3) Personal fur- 

 therance (susceptibility of the diseased individual). 



Sorauer in the first edition of his "Manual of Plant Diseases," Berlin, 

 Paul Parey, 1874, first introduced into plant pathology the view, that in all 

 diseases not only the direct cause but also the earlier preparatory stages and, 

 in parasitic attacks, the accessory conditions favoring the development of the 

 parasites, including the disposition of the host organism, should be taken 



1 Phytopathologie. Die Krankheiten der Kulturg-ewachse. T^eipzig 1868. 

 - Die Plastiden der niederen Pflanzen. Leipzig' 1895. — Die Pestkrnnkheiten 

 (Infektionskrankheiten) der Kulturgewachse. Stuttgart 1895. 



