l86 BACTERIA IN RELATION TO PLANT DISEASES. 



poured plates indicate the presence of a physiologically similar organism in both 

 plants. The first inference is that the two diseases are caused by the same organism. 

 A test-experiment is now instituted, viz, one or two varieties of B are inoculated 

 with the organism obtained from A, but these do not contract the disease. An 

 easy second inference now is that we are dealing with two distinct diseases. This 

 may be perfectly correct, but it is not established by the experiment. Owing to an 

 oversight, plants of A were not inoculated at the same time and in the same man- 

 ner as B, to serve as checks, and consequently we are not assured as to the virulent 

 nature of our culture it may have been dead, or non-virulent, or the wrong organ- 

 ism. Check-plants should have been inoculated. Assuming, however, that this was 

 done, and that A promptly contracted the disease while B remained unaffected, it is 

 not yet certain that the disease in the two plants is due to different organisms. The 

 question of individual and varietal resistance to disease may have entered to com- 

 plicate results. To eliminate this possible source of error a greater number of 

 varieties of B should be tested with a larger number of individuals in each variety. 

 Cross-inoculations should also be made, i. e., numerous varieties and individuals of A 

 should be inoculated with the organism isolated from B. 



Enough has been said to show the ordinary method of work. All inferences 

 should be carefully confirmed by frequent poured-plate cultures in Petri dishes, by 

 cultivations on the media which have been found to give most characteristic results, 

 and, finally, by frequent inoculations into the host-plants. In case of unexpected or 

 striking results it is always safe to determine whether they can not be obtained in 

 the absence of the assumed cause. 



These methods involve an almost endless amount of drudgery, but they are 

 fundamental to any large success in the domain of pathology, and those who are 

 desirous of winning a shining reputation without much labor are advised to culti- 

 vate some easier science. For those who are really in earnest, who do not mind 

 hard work, and who have acquired the requisite training, no field affords greater 

 opportunity for brilliant and useful work than that of plant pathology. 



