THE BLACK ROT OF CRUCIFERS : TECHNIC 149 



Technic. — The organism is easily isolated on agar-poured 

 plates inoculated from suitable material, e.g., cabbage petioles. 

 There are no special difficulties except that sometimes heavy- 

 sowings are necessary when the organism has been in the tissues 

 a long time. If difficulties are encountered, the second method 

 described under No. I may be tried. The bacteria grow readily 

 on all ordinary culture-media; steamed potato is a good sub- 

 stratum. 





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Fig. 86. Fig. 87. 



Fig. 86. — A. Cross-section of a cabbage petiole, showing only two infected 

 and blackened bundles, and correspondingly only a small area in the center of the 

 blade of the leaf was diseased. 



B. Cross-section of a cabbage petiole showing every bundle blackened by 

 Bacterium campestre, and correspondingly all of the leaf-blade was diseased. Same 

 series of inoculations as A, 1915. 



Fig. 87. — Section of the fleshy part of a kohlrabi showing black bundles due 

 to Bacterium campestre. Collected liy the writer in Floritla in 1904. 



For inoculation purposes use young plants of cabbage, turnip 

 or cauliflower. The same hothouse cultural directions apply as 

 for cucumbers, etc., under No. I. 



For contrast the resistant Houser cabbage may be used. 

 Several hundred plants should be provided, and they must be 

 kept free from insects and molluscs. The seed should be sown 

 at least six weeks before the plants are needed. 



