hygiene, will finally come to full recognition. Primarily, we must learn to 

 protect the organism from disease, and then, through force of necessity, may 

 take steps to heal an organism which is already diseased. 



In the first volume, the first section of the introduction treats of the na- 

 ture of disease, while the second takes up the history of its investigation. It 

 should be understood by the term "historical" that I did not wish to write a 

 history of phytopathology, which would have taken much more thorough pre- 

 liminary study, but did consider it desirable to attempt to sketch the process 

 of the development of this branch of knowledge, in order to show how the 

 present point of view had developed in the course of time. 



In looking through the specialized part, the reader may also find that 

 even in the present edition conclusions once based on a considerable number 

 of my own investigations have been abandoned. The aid of illustrations, so 

 absolutely necessary in phytopathology, has been made use of to an appreci- 

 ably larger extent in describing diseases. In accordance with the character of 

 the book, new anatomical drawings especially have been added. In the vol- 

 ume on parasitic diseases many tables have been gathered together for the 

 sake of comparison, in order to make clear to the reader the different genera 

 of one family in their distinctive characteristics. 



The new drawings were made by Fraulein H. Detmann and Friiulcin E. 

 Lutke, whom I thank very much for their work. 



Most of all, however, I wish to thank my collaborators. With me, they 

 had to solve the difficult problem of presenting the material in a space deter- 

 mined by contract before the revision. During the revision, we found our- 

 selves confronted by the question either of giving to the whole subject a 

 briefer form than was originally intended, or of working up some chapters 

 in detail while summarizing others. We chose the latter course and treated 

 the seemingly most important sections thoroughly and the groups, which had 

 been sufficiently worked over in other books, in a correspondingly limited 

 way. 



Schoneberg, October, 1908. 



PAUL SORAUER. 



