Bacteria in Relation to Plant Diseases. 



BY ERW1N F. SMITH. 



INTRODUCTION. 



This volume really begins the subject of bacterial diseases of plants, the first volume 

 having had for its aim only the clearing of the ground by a discussion of methods of work 

 and the general subject of bacteriology. Whatever in that volume relates to specific dis- 

 eases of plants was introduced merely by way of illustration, or to provoke interest in what 

 should follow. 



The first part of this second volume deals with general questions relative to bacterial 

 diseases of plants; the history of the subject, the distribution of bacteria on the surface of 

 plants, the questions involved in the terms parasitism and symbiosis, the action of the 

 bacteria on various tissues, the reactions of the plant, the interrelations of animal and plant 

 parasites, and, finally, the problems relating to prevention. The wilt of cucurbits, the 

 black rot of crucifers, and the yellow disease of hyacinths are then dealt with in separate 

 chapters. 



In researches of this kind, covering as they do a relatively new and rapidly enlarging 

 branch of science, the point of view changes with great frequency. To-day the interest 

 will be centered on one phase of the subject, to-morrow, perhaps, on some quite different 

 aspect. Fortunate for the experimenter if the new aspect do not require entrance into 

 unfamiliar fields of discouraging complexity. For anyone to cover adequately by the 

 experimental method a whole branch of science if it be a large one, is manifestly impossible. 

 There will always be portions slurred over. The best that one can do is that which I have 

 tried to do, viz., to point out at frequent intervals gaps in our knowledge, to express things 

 clearly and honestly, to distinguish between verified fact and speculation, and, finally, to 

 leave each subject in somewhat better shape than I found it. 



The following pages are based in great part on data obtained as the result of a multi- 

 tude of experiments made by the writer and his assistants, but all sources of published 

 information have been considered. 



During the writing of this monograph it has often happened that the ink on some 

 chapters would scarcely be dry before the results obtained from new experiments would 

 require some part of it to be rewritten. In this way during the last ten or fifteen years the 

 subject has been worked over and over, some chapters being rewritten a dozen times, in 

 whole or great part. This, while greatly increasing the scientific value of the work, has 

 certainly not tended to improve its style. 



The long period covered by these experiments must also serve to explain why the 

 description of particular organisms does not in all respects follow the recommendations of 

 the chart recently issued by the .Society of American Bacteriologists, many of these studies 

 having been completed before that was begun. To make them all conform would delay 



