66 PRESIDENTIAL ADDRESS SECTION C. 



About this time Dr. Erwin F. Smith pubHshed his earlier 

 work on bacterial diseases of plants: in i(S95 (49) he described 

 a bacterial disease of cucumbers, cantaloupes, and sc|uashes, 

 caus'ed by Bacillus trochcipJiiliis, a peritrichiate bacillus which 

 occupies the spiral vessels and tracheids. In i<Sy6, he confirmed 

 the work done by Pammel on the brown rot of cruciferous 

 plants, caused by Bacterium campcstre (56a) ; and in the same 

 year (50b) published his investigations into the wilt of potato 

 and tomato plants caused by Bacterium solanacearum. Stewart's 

 work on bacterial disease of sweet corn also ai>peared about this 

 time. 



The j)arasitism of each of the above organisms had been 

 conclusively established, the evidence being- based on very careful 

 work along the lines suggested by Koch's premises : the organism 

 had been found constantly associated with the disease, and had 

 been isolated and studied in pure culture ; the characteristic 

 symptoms had been reproduced by inoculations with pure 

 cultures, and the organism recovered from plants so inoculated. 



Migula, in his "System der Bakterien " (8c)) accepted the 

 evidence submitted by various phyto-pathologists, and admitted 

 that a number of bacterial diseases of plants had been established, 

 but still considered that the cell walls of j:)lants present great 

 difficulties to the entrance of bacteria, and that stomatal infection 

 is generally impossible. 



Fischer (24), however, in the same year, in spite of available 

 evidence, expressed the opinion that, " exclusive of the tubercle 

 bacteria .... no single example is yet known of bacteria 

 which can insinuate themselves into the closed cells of a living 



plant From the bacillary gummosis of the grape vine 



to the scab of the potato, all so-called bacterial diseases of plants 

 are of other origin, the bacteria being only saprophvtic con- 

 taminations." 



Dr. Erwin F. Smith, whose investigations have gone so far 

 to place phvtobacteriology on a sound basis, took up the challenee, 

 and (1899) i" ^he controversy which followed, showed the 

 completel}^ erroneous nature of Fischer's statements and 

 " unwarranted assumptions " ; since iQOi no one has ventured 

 to question the existence of bacterial diseases of plants, and 

 although the field is comparatively new, and in many parts of 

 the world still untouched, " such diseases have been retK)rted from 

 every continent, and are already known to occur in plants of 

 one htindr^d and fortv genera, distributed through more than 

 fifty families" (52"). 



Workers in this field are now fairlv numerous, although 

 students of plant pathology are usually attracted to the myco- 

 logical rather than the bacteriological side of the subject, owing 

 to the immense amount of routine work and the vast amount of 

 patience demanded bv the latter. However, a number of phvto- 

 pntholoo-i^t'? narticularlv in America, have made a soecial study 

 of bacterial diseases, and there is a considerable amount of recent 

 literature on the subject. 



