Family Cruciferae 191 



found that the infection takes place through small 

 openings naturally found on the leaves and known as 

 water pores which are found scattered over the teeth 

 of the leaves. ' Infection by means of insect bites is 

 also a very common occurrence. Outbreaks of black 

 rot in new fields may undoubtedly be traced back 

 to the use of infected manure. Black rot also at- 

 tacks broccoli, Brussels sprouts, cauliflower, char- 

 lock, collard, kale, kohlrabi, black mustard, rape, 

 rutabaga, radish, sweede, and turnip. 



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 (fig. 30 e). It is found single or in pairs 

 and produces no spores. It liquefies gelatine com- 

 pletely in about fifteen days. On agar plates the col- 

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

 On potatoes a copious growth is produced with 

 no odor and no browning of substances. The in- 

 vestigations of Harding 1 and others have proved 

 that the black rot germ may be introduced into the 

 seed bed and into new fields from infected cabbage 

 patches. The virulence of black rot is largely de- 

 pendent on the weather. It is unfortunate that 

 favorable weather conditions for the cabbage plants 

 are also favorable for the disease. 



Control. Before planting, cabbage seed should be 

 disinfected for fifteen minutes in a solution of ]^ pint 

 of pure (40%) formaldehyde diluted in seven gallons 



1 Harding, H. A., New York (Geneva) Agr. Expt. Sta. Bui., 

 251: 178-194, 1904. 



