B. P. I.-37. V. V. V. I.-9.S. 



THE EFFECT OF BLACK ROT ON TURNIPS." 



INTRODUCTORY 



Very few persons would now huvc the hardihood to deny the exist- 

 ence of phmt diseases due to bacteria, l)ut great ignorance still exists 

 respecting this class of diseases, and particularly respecting the capac- 

 ity' of these })acteria for destroying cell walls and making their way, 

 unaided by other organisms, from one part of the phmt to another. 

 Even so good a phyNiologist as H. ^Marshall Ward, in so recent a hook 

 as Disease in Plants (IHOO). knows nothing ul)out the destruction of cel- 

 lulose by l)acteria, and is inclined to think that, in most cases of " ))acte- 

 rmV disease, fungi act as carriers of the bacteria or forerunners. 



The writer has found so much of interest attached to the study of his 

 slides that he is prepared to believe that photographs of them will be 

 of more or less general scientific interest. The behavior of Pseudo- 

 monas campedris when inoculated into cruciferous plants is not unique,, 

 and this particular organism has been selected accidentally, rather than 

 for any special reason, to illustrate what I have to say at this time. 

 The writer possesses alcoholic material of equal interest from many 

 kinds of plants inoculated with various bacteria and a single turnip 

 plant attacked by one organism has been selected for these illustrations, 

 principally because the material proved excellent and appeared to be 

 sufficient for the purpose in hand. The figures will also serve to illus- 

 trate how much ma}' be learned from the careful examination of a 

 single specimen. 



The following study is purely morphological, and it, of course, raises 

 various questions which can be settled only by the isolation of a cytase. 

 Judging by the time required for cruciferous plants to get into the 

 condition shown in inoculated plant No. 53,* the enzymic action on 

 the cell walls must be rather slow, and experimental evidence with the 

 precipitated substances containing the enz3'me would probably be less 

 readily obtained than in case of those bacteria which act on the tissues 

 ver}' rapidl}'. The isolation of the enzyme, and the study of its action 

 were tempting subjects, but the writer's time was very fully occupied 

 with other matters, and the requisite leisure could not be found. This 



« This disease is also called brown rot. 



&The plant from which sections were cut for nearly all of these illustrations. 



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