PREFACE TO SECOND EDITION. 
Since the publication of the first edition of this work advance 
along all lines of bacteriology has been very rapid. Scarcely a 
phase of the relation of bacteria to agriculture has failed to receive 
substantial contributions. Much new information has been 
obtained, the relative importance of different subjects has been 
changed, and in a few points our previous conclusions have been 
corrected. These changes have been so considerable that in 
preparing this second edition it has been found necessary to rewrite 
the whole book in order to bring it up to the times. The subject has 
grown so large that it is difficult to include within the limits of one 
volume even the fundamental facts of the rapidly growing science, 
and many subjects of importance have been treated very briefly. 
The growing recognition of the importance of the subject to 
students of agriculture has caused agricultural schools and col- 
leges to give to it an increasing amount of attention. For this 
reason this edition has been planned with special reference to its 
use by classes; and some changes in method of presentation have 
been adopted in order to make it more useful to students. For 
the same reason there has been added a somewhat extended set of 
experiments for elementary laboratory work. These laboratory 
directions are far from exhaustive and are designed simply to intro- 
duce the student to the methods of bacteriological work. 
The close relation of the functions of the higher fungi to the 
functions of bacteria has come to be fully realized to-day and has 
made it necessary to include more extended references to the higher 
fungi in this review. The only other important addition in this 
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