Cauliflower Diseases 125 



which cannot easily be confused with other diseases. 

 On the leaves, the symptoms are manifested as a 

 burning appearance on the edges and a yellowing 

 of all the aflFected parts except the veins, which re- 

 main blackened. Frcxn the margin of the leaves, the 

 disease works downwards to the stalk. Frcttn there 

 it travels up again to the stems and leaves. The 

 parasite works in the fibrovascular bundles of the 

 leaves and main stalk, causing a premature defoli- 

 ation. Occasionally, the disease enters one side of 

 the stalk, the latter beccwning dwarfed and the cauli- 

 flower head grows one-sided. In severe cases of 

 attack, there is a total lack of head formation. Upon 

 splitting open a stump of an affected plant, one finds 

 a black ring which corresponds to the places of the 

 fibrovascular bundles invaded by the organism. In- 

 fection takes place through small openings naturally 

 found on the leaves and known as water pores which 

 are scattered over the teeth of the leaves. Infec- 

 tion by means of insect bites is also a very cranmon 

 occurrence. Outbreaks of black rot may undoubt- 

 edly be traced back to the use of infected manure. 

 Black rot also attacks greenhouse radish. 



The Organism. Pseudomonas campestris is a rod- 

 shaped organism, slightly longer than it is broad. 

 When young it is actively motile by means of long 

 polar flagella. It is found single or in pairs and 

 produces no spores. It liquefies gelatine completely 

 in about Kteen days. On agar plates the colonies 

 are round, yellow in color, and the margin entire. 



