63 



into consideration. This statement was definitely established in the second 

 edition (1886) and in an abstract written especially for tlie practical agri- 

 culturalist, "Die Schaden der einheimischen Kulturpflanzen," 1888. The 

 delayed acceptance of these ideas is shown by the text-books which im- 

 mediately followed. Of these the one especially valuable because of its num- 

 erous personal investigations is "Lehrbuch der Baumkrankheiten" by Robert 

 Hartig, Berlin 1882 (2nd Ed. 1889). The third edition, in which the 

 author rather unreservedly acknowledges a predisposition and differentiates 

 local, temporal, individual, acquired and morbid predisposition, appeared in 

 1900 wuth the title "Lehrbuch der Pflanzenkrankeiten" — Berlin, Julius 

 Springer. A study of the phenomena of the decomposition of wood, with 

 the title "Wichtige Krankheiten der \A^aldbaume," Berlin 1874, is an intro- 

 ductory work for this textbook. 



Sorauer's Manual was followed first by Frank's detailed elaboration, 

 "Die Krankheiten der Pflanzen," Breslau 1880 (2nd Ed. 1895). The 

 "Lehrbuch des Forstschutzes" by H. Nordlinger, Berlin 1884, is devoted 

 especially to cultivated forest plants. Solla's book, "Note di Fitopathologia." 

 Firenze 1888, is more comprehensive and contains an atlas. This was pre- 

 ceded in Norway in 1887 by Brunchorst's "De vigtigste Plantesydomme." 

 To this decennium belongs also a number of noteworthy articles by Jensen, 

 among which (according to Rostrup) is: "Kartoffelsygen kan overvindes 

 ved en let udforlig Dyrkningsmaade," Kjobenhavn 1882. 



While up to this time scientists had classified diseases according to their 

 proved or assumed causes, Kirchner in 1890 published "Die Krankheiten und 

 Beschadigungen unserer landwirtschaftlichen Kulturpflanzen," Stuttgart, 

 arranged especially for practical use. The diseases are listed here ac- 

 cording to the dififerent cultivated host plants and described according to 

 their visible habit of growth. Systematic scientific supplements are collected 

 at the end of the book. In accordance with the line of investigation of this 

 author there appeared in 1S95 a richly illustrated book treating of parasitic 

 diseases only,— "Pflanzenkrankheiten, durch kryptogame Parasiten verur- 

 sacht," by Karl, Freiherr v. Tubeuf, Berlin, Julius Springer. Parastism was 

 here developed as a form of sym.biosis and thereby referred to an "internal 

 and an external" predisposition for becoming diseased. The internal predispo- 

 sition depends on "the energetic condition of the living protoplasm of the host 

 cell," while the external one "is determined especially by anatomical condi- 

 tions." In the same year Prillieux published a two volume work abounding in 

 personal investigations, "Maladies des plantes agricolcs et des arbres fruiticrs 

 et forestiers," Paris. This, the most comprehensive work in French on the 

 subject, describes only parasitic diseases. They are treated scientifically and 

 yet the practical side receives attention in so far as means for combatting 

 disease are considered. 



An unlooked-for advance in the studies on bacteria resulting from their 

 many-sided economic significance, made a revision and enlargement of de 

 Bary's "Vorlesungen iiber Bakterien," necessary. In 1900, in Leipsic, Mig- 



