150 PLANT PATHOLOGY 



its form. A representative work of the early school of pathologists 

 is by von Zallinger of the Austrian Tyrol, whose treatise De mor- 

 bis plantarum appeared in 1773. It is a scholarly and compre- 

 hensive work. Here are some of the topics considered: In what 

 does the life and death of plants consist? Plants have diseases; 

 wherein lies the health of plants? What may be called a disease 

 of plants ? Unfavorable appearances are indications of disease ; how 

 many general symptoms of diseases may be found? How many 

 groups of diseases are there? If I should continue, it would soon 

 appear that the work culminates in a classification of diseases based 

 upon symptoms. The fundamental idea of the work is that when 

 symptoms are correctly understood, knowledge of the disease fol- 

 lows with certainty, and treatment may be prescribed accordingly. 

 The classification of diseases, as stated by the author, follows that 

 of contemporary medicine, modified by the methods introduced 

 by Tournefort and Linnaeus. There are five general classes, divided 

 into nineteen orders and eighty-four genera. Thus the second class is 

 called Paralyses, and is divided into four orders: Anorexice, Adynamia 

 excretionum, Anaphrodisice, and Commata. The last order, Commata, 

 embraces three genera, Apoplexia, Lethargus, and Lethargus gcmmarum. 

 It is easy to see from the vantage-ground of present knowledge that 

 this is more a classification of ideas than of facts. In truth, although 

 the author recognizes the value of a knowledge of causes, the w r ork 

 does not touch upon the true etiology of any disease, and furthermore 

 does not suggest a single prophylactic or therapeutic measure of even 

 meager worth. 



A similar work to the preceding is the second part of J. J. Plencks' 

 Physiologia et Pathologia Plantarum, published at Vienna in 1794. 

 But a more progressive work, in that it exhibits a better acquaintance 

 with conditions in nature, is that of the Freiherr von Werneck, head 

 forester, who lived in the Rhine provinces, and in 1807 published 

 a Versuch einer Pflanzen-Pathologie und Therapic. Von Werneck 

 philosophized thus: The simpler composition a body has, the fewer 

 driving-wheels contribute to its action, but also the briefer, more 

 obscure, and more involved is the chain of causes that lie at the basis 

 of the movement. In order to be able to recognize each simple driving- 

 wheel, or, what is the same thing, each simple cause, we must know 

 the full connection of each simple condition and the value of the 

 contribution of each simple ingredient to the whole. But the incom- 

 pleteness of our knowledge of the plant body makes this determina- 

 tion of simple causes impossible. 1 The author goes on to distinguish 



1 Je einfnchor zusammengesetzt ein KSrper ist, je weniger Triebrader zu seiner 

 Bewegung beitragen, je kiirzer aber auch, je dunkler und verwickelter ist die Kette 

 von Ursachen, welche den Grand der Bewegung enthalten. Um jedes einzelne 

 Triebrad, oder welches einerlei ist jede einzelne Ursache bestimmen zu 

 konnen, miissten wir den ganzen Zusammenhang jedes einzelnen Verhaltnisses und 



