8o8 bacteria: their work 



When the stems are cut across, a white milky slime, which can 

 be drawn into long threads, exudes from the exposed ends of the 

 vascular bundles. 



The specific bacterium which causes the disease is Bacillus 

 tracheiphilus E. F. Smith. It is a short bacillus often met with 

 in pairs. The organism obtains an entrance into the leaves 

 and works its way into the stem along the vessels of the wood 

 of the vascular bundles. 



It may finally permeate the other tissues of the stem, and 

 cause a shriveUing of this part of the plant. 



1 6. A further example of a plant disease of bacterial origin is 

 the ' Brown rot ' of the potato and tomato caused by Bacillus 

 solanacearum E. F. Smith. At first the leaves of affected plants 

 droop: subsequently the stems become brown and the tubers 

 may eventually be damaged. In this case also the stems show 

 discoloured vascular bundles, and a yellowish white liquid con- 

 taining myriads of bacteria oozes out of the ends of the bundles 

 when the stems are cut across. 



