6 



BACTERIA IN RELATION TO PLANT DISEASES. 



In the present state of our knowledge (i) and (2) can usually be considered 

 only after a very careful study of (3), (4), and (5), and of the organism itself. They 

 involve a knowledge of modern languages, and a very considerable familiarity with 

 scientific literature. 



Previous Literature. 



One of the first requisites in a student is a knowledge of how to use literature. 

 Previous literature is, however, often of such a fragmentary and uncertain sort, as 

 we shall see, that it is impossible to decide whether a disease is actually new or has 

 been written upon before. 



Fig. 3." 



The literature of plant diseases will not be referred to in this \-olume, except 

 occasionally and incidentally. The bibliography of this volume deals onl^■ with 

 general bacteriolog}- — human and animal diseases, methods of work, etc. 



*FiG. 3^A det.-iil frdiii fig. 2. Bacillus carolnvnrns wedging apart cells of the carrot. Hi-awn 

 ■mostly from one plane. In placing the cover-glass a few of the bacteria have been crowded out of 

 the intercellular spaces into parts they did not origina:lly occupy. X 1,000. 



