BLACK ROT OF CRUCIFEROUS PLANTS. 



305 



In Wisconsin, Russell & Harding repeated the experiments of Pammel, and of Smith, and 

 confirmed their conclusions respecting the bacterial nature of the disease. Harding also 

 studied the morphology and physiology of the organism quite carefully. The number of 

 their successful infection experiments amounted to several hundred. In New York and in 

 Europe, Harding subsequently continued his studies. On his return from Europe he 

 obtained numerous successful infections on cabbage and cauliflower with a culture which 

 he isolated from a diseased cabbage-plant found by him in Switzerland. Comparative 

 tests were also instituted and neither in its cultural characters nor in its infectious proper- 

 ties was any difference detected between the Swiss organism and the one from New York 

 or Wisconsin. 



Hecke subsequently discovered the disease in kohlrabi in Austria and published two 

 instructive papers on it, the number of his 

 infection-experiments exceeding 100, Rus- 

 sell, however, was the first to obtain the 

 disease in kohlrabi by inoculations (Bull. 

 65, p. 22). Van Hall then studied it in 

 cabbages in Holland. More recently 

 Brenner in Basel, under direction of Dr. 

 Alfred Fischer, investigated the etiology 

 of this disease, and after experimenting 

 for two seasons states that he can only 

 confirm Smith's conclusions respecting the 

 cause of this disease. 



The writer has himself isolated this or- 

 ganism from diseased plants obtained 

 from Illinois, Wisconsin, Michigan, Ohio, 

 Pennsylvania, Western New York, Long 

 Island, Maryland, Alabama, Florida and 

 Texas, and has studied the disease in the 

 field in half a dozen different States. He 

 has also produced the disease in cabbage 

 by inoculating with a pure culture of the 

 organism received from Hecke, who iso- 

 lated it from kohlrabi grown in Southern 

 Austria and himself proved its infectious 

 nature on a variety of crucifers. In most 

 of the above mentioned isolations by 

 means of poured plates, Bacterium cam- 

 pestre was found in the vessels of the 

 plants in pure culture. Only occasionally 

 were mixtures obtained and even then the yellow organism was the preponderant form. 



Plants are attacked by this disease in all stages of growth from seedlings in the seed- 

 bed to plants ready for the market. In all this class of plants most of the infections, perhaps 

 all of them in plants beyond the seedling-stage, are through the parts above ground and 

 generally by way of the leaves. The writer, who has spent many weeks in cabbage-fields, 

 has never seen anything in midsummer or later suggestive of infection through the root- 

 system, i. c, roots diseased and parts above ground not diseased, and Hecke's experiments 

 of growing plants in soil mixed with tissues swarming with the organism, yielded only nega- 

 tive results. So did my own. Brenner also made similar experiments with similar results: 



Fig. 103.* 



*Fig. 103. Longitudinal section and cross-sections of stems of cauliflower diseased by Bacterium campestre, 

 showing stain and cavities in the stems. Miami, Fla., March, 1904. 



