HISTORY AND SCOPE OF PLANT PATHOLOGY 153 



abundant at the last of this period, but were chiefly by German 

 and Austrian botanists. The best of these were by linger in 1833, 

 Wiegmann in 1839, Meyen in 1841, and Nees von Essenbeck in 1842. 

 In these and other works an enumeration and consideration of the 

 parasitic fungi occupied half or more of the space. It must not be 

 inferred, however, that any clear notion had yet developed regard- 

 ing the relation which parasitic fungi hold to the host and to the 

 accompanying disease. Throughout this period it was generally 

 maintained that their existence was conditioned by the host. At 

 first it was thought that parasitic fungi could not be reproduced by 

 their spores, but were generated by the fermenting sap of the plant, 

 or by a transformation of the perverted tissues. When it became 

 clear that the spores did reproduce the fungus, it was still asserted 

 that the fungus was a product of the disease and that its form was 

 dependent upon the kind of host, or upon the state of the host at 

 the time it was attacked by the disease. Endophytic species were 

 frequently called pseudo-organisms, and the opinion was general 

 that they might be transformed from one kind into another, accord- 

 ing to the state of the weather, degree of moisture, amount of nu- 

 trition supplied by the host, or other uncertain factors. 



It is not a part of the speaker's purpose to sketch the history of 

 plant pathology, but in a perspective outline to trace the dominant 

 influences that at successive stages of the science bore strongly 

 upon the course and rapidity of its development. We have seen 

 that prior to the beginning of the nineteenth century the science 

 had so little knowledge at command that it might be said to be in its 

 helpless infancy. During the first half of the nineteenth century 

 it made rapid growth, nourished by the pabulum derived from the 

 studies of plant structure and function, and from the systematic 

 study of fungi, although harboring many erroneous beliefs. This 

 period may be looked upon as a lusty childhood, full of activity and 

 promise, but guided by unstable and imperfect theories. The next 

 period extended from about 1850 to 1880, during which there was 

 accumulated much positive knowledge of the fundamental features 

 of the science that gave substantial basis for coming usefulness. 

 It was a period of youth, to be followed by the period of established 

 maturity. 



The greatest single service rendered to pathology during this 

 interim of thirty years was performed by De Bary in establishing 

 the fact that healthy plants may be attacked and penetrated by 

 fungi, which may there flourish and propagate, thus disproving 

 the long-held theory that parasitic fungi were emanations of the 

 higher plants. This did not lead at once to a full understanding of 

 parasitism, but it cleared the way for an intimate study of the 

 endophytic fungi. In this line of research De Bary was unmistakably 



