DIVISION VI * 

 MICROBIAL DISEASES OF PLANTS. 



INTRODUCTION. 



Although the earliest study of bacterial diseases in plants antedates the 

 isolation of the tubercle bacterium and the cholera spirillum, this branch 

 of bacteriology has not been marked by the progress which has character- 

 ized the investigation of animal diseases. The loss of a human life or 

 of a valuable domestic animal has appealed to the student of disease 

 more strongly than the blighting of a pear tree, or the wilting of a potato 

 vine, and, quite naturally, he has directed his efforts along those lines 

 which have offered the greater inducements, and which have demanded 

 immediate attention. 



However, with the introduction of new plants, foreign seeds, and 

 strange nursery stock, many previously unheard-of plant diseases have 

 made their appearance. As the farming communities have become more 

 thickly populated, with less uncultivated land between the fields, these 

 diseases have spread from farm to farm more rapidly than in the earlier 

 days, and the losses from these causes have been so heavy during the 

 past decade that the farmers, gardeners and orchardists have come to 

 the Agricultural Experiment Stations all over the country for advice and 

 assistance in combating their troubles. This has stimulated an increased 

 interest in plant diseases, especially along bacteriological lines, with the 

 result that to-day some thirty bacterial diseases of plants have been 

 described. 



It is a matter of not infrequent observation that closely related species 

 of plants, as well as animals, exhibit a marked difference in their suscep- 

 tibility to the same disease-producing agents. The Bartlett pear, for 

 example, suffers more severely from blight than the Kieffer, and, among 

 apples, the Toleman Sweet more than the Rome; the small-leaf, stemmy 

 varieties of tobacco seem to be more resistant to the Granville Wilt than 



* Prepared by W. G. Sackett, except a protozoal disease " Fingers and Toes " by J. 

 L. Todd. 



490 



