59 



isms, but maintained that "it is the stomata which take up the spores and 

 bring them to development in the air cavities connected with them." He said 

 that algae, lichens and mosses which have no stomata and, for the same rea- 

 son, young branches and twigs are free from parasites. He expresses his 

 point of view in regard to the action of parasites, as follows : — "That they 

 6rst cause an hypertrophy and degeneration of the parts heavily infested with 

 them but when isolated they do not disturb the growth of the leaves." Ac- 

 cording to him, dry weather is essentially propitious for the spread of the 

 parasites, "because it favors the scattering of the spores. On this ac- 

 count Caeoma and Phragmidium are never found more abundant than in 

 dry summers, as also the Caeoma ccrcalium, the yellow corn smut so in- 

 jurious to seeds, which caused such great damage in 1846." 



Kiihn in his "Krankheiten der Kulturgewachse" (Berlin 1858) attained, 

 in the happiest manner, the end for which Meyen strove, viz. of uniting 

 scientific studies with practical experience in the treatment of plant diseases. 

 However necessary and important purely scientific investigations may always 

 be in phytopathology, yet they achieve their full significance only by being 

 tested in practical agriculture. Only by practical work can it be decided 

 whether the conditions of nature and of the laboratory favor the develop- 

 ment of the same parasites or other excitors of disease. So it is necessary to 

 build phytopathology upon a practical knowledge of agriculture and horti- 

 culture. The differences which have developed in medicine between 

 the scientific investigator and the practicing physician must also necessarily 

 arise in the science of plant diseases. We term this practical side, — the pro- 

 fession of "Plant Protection." 



Mycological studies are a part of the indispensible fundamentals of plant 

 protection and for this reason, we have given them the greatest possible at- 

 tention in the history of phytopathology. Continuing with this in view we 

 will name first of all the masterly plates in the book by the brothers Tulasne 

 "Selecta fungorum carpologia," Paris. The English work by Berkeley 

 "Outlines of British Fungology," London i860, is most welcome as a col- 

 lective work although it is mostly provided with very rough illustrations. 

 De Bary's works continue to be of especial value. His results in this con- 

 nection may be found summarized in the "Morphologic und Physiologic der 

 Pilze, Flechten und Myxomyceten," Leipzig 1866. 



We owe further important investigations to O. Brefeld, in his "Unter- 

 suchungen iiber die Schimmelpilze," Leipzig 1871, 1872 and following, and 

 Cohn for his "Biologische Mitteilungen iiber Bakterien," Schlesische Ges. f. 

 vaterl. Kultur, 1873, as well as for his "Untersuchungen iiber Bakterien" 

 1875 and for other studies contained in his "Beitrage zur Biologic der Pflan- 

 zen." In these Cohn has successfully advanced the history of the develop- 

 ment of Bacteria. His pupil, Zopf, essentially extended these studies in the 

 work "Die Spaltpilze," Breslau (3rd Ed. 1885). Among the summaries of this 

 time mention should be made of Eidam "Der gegenwartige Standpunkt der 

 Mykologie mit Riicksicht auf die Lehre von den Infektionskrankheiten," 



