BACTERIA 511 



and if the stem of a diseased plant is cut across, the vascular 

 system also shows up as a black ring. The bacteria enter the 

 leaf through certain minute openings water stomata present 

 along the margin, where they rapidly increase in numbers and 

 work along the veins, and down the leaf-stalk into the stem, 

 from where they soon pass out into other leaves. The 

 bacteria also enter the leaf through wounds made by insects, 

 by whom they are also conveyed from one plant to another. 



Smith fed slugs on diseased cabbage leaves, and afterwards 

 placed the slugs on healthy leaves, on which the disease 

 appeared a week or two later. 



When the soil is infected the germs also pass into young 

 plants through broken roots at the time of transplanting. 

 Diseased plants soon collapse with soft rot and form a 

 loathsome, foul-smelling mass. 



Harding, Stewart, and Prucha have proved by an extensive 

 series of experiments that the bacterium causing black rot of 

 cabbages, etc., can survive the winter on the seed, and that 

 much of the cabbage seed on the market is contaminated 

 with germs, which may become a source of infection to the 

 young cabbage plants. 



Diseased plants should be removed and buried along with 

 gas-lime, or burned. Such plants can readily be detected by 

 the black veins, and by the black points in the tissue when 

 the leaf-stalk is broken across. 



Respecting the seed, Harding says : ' As a precautionary 

 measure, it is advised that all cabbage seed be disinfected 

 before sowing, by soaking for fifteen minutes in a 1-1000 

 corrosive sublimate solution or in formalin, one pound to 

 thirty gallons [water]. It is not expected that this treatment 

 will prevent either leaf or root infection in infected soils ; but 

 it may be safely relied upon to prevent all danger from 

 infected seed. It will not injure the germination.' 



I have observed that rape is most susceptible to this 

 disease in England ; in one extensive trial plot of various 

 kinds of cabbages, savoys, etc., those that were known to 

 have a certain amount of ' rape blood ' in them were first 

 diseased, whereas those free from this element were the last 

 to succumb. 



Smith, E. F., Zeitschr. fiir Pflanzenkr., 8, p. 1. 

 Harding, H. A., Stewart, F. C, and Prucha, M. J., New 

 York Agr. Exp. St., Bull. No. 251 (1904). 



