BACTERIAL DISEASES OF PLANTS 



277 



eased plants and reinoculated into healthy plants producing 

 the identical disease. These experiments are conclusive, 

 and no substantiation exists for the foregoing statements of 

 Fischer, et al. No preinvasion by a fungus is necessary. It 

 is not uncommon, however, to have a distinct fungus disease 

 in plants (rusts, etc.). ' 



It must be recognized that the signs or symptoms of bac- 

 terial diseases in plants 

 are in the main quite sim- 

 ilar. This is particularly 

 true of the bacterial rots. 

 Sometimes careful study 

 is necessary in order to dis- 

 criminate between these 

 various "rots" (Fig. 53). 

 Some of the bacterial dis- 

 eases of plants have been 

 proved to be transmitted 

 from plant to plant by 



means of the bites of in- FlG . 54 . _ Bacterium campestre in turnip 



root - (Vascular occlusion.) After Smith. 



It has been noted that the bacteria which produce the 

 various plant diseases secrete an enzyme which dissolves the 

 cellulose of the cell wall. The action of these enzymes is 

 slow in comparison with those of the bacteria pathogenic to 

 animals. About one hundred and twenty-five separate 

 diseases of plants have been recognized thus far. 



