New York Agricultural Experiment Station. 91 



soil in competition with the other forms found there. However, 

 several attempts to isolate this organism from soil supposed to 

 be infected have failed. On account of the large number of 

 other forms present in soil a small number of P. campcstris would 

 be easily overlooked. 



The first leaf infections take place in the outer leaves, which 

 often come in contact with the soil. Later, infection occurs on 

 the more central* leaves which could hardly have been directly 

 infected in this way. In the latter case the germs must have 

 been carried to the water pores either .by insects or air currents. 

 In either case the germs would have been exposed to a consider- 

 able amount of dessication, something which they seem to be 

 little fitted to withstand. 



So far as is definitely known the transfer of the disease from 

 one field to another is connected with the transfer of portions of 

 diseased plants. The wind carries parts of diseased leaves for 

 considerable distances. Along water courses in times of freshets 

 the water deposits both soil and plant remains. By feeding to 

 animals or otherwise disposing of rubbish, parts of diseased 

 plants are often carried out upon new fields. 



The disease sometimes appears in fields where none of the 

 cabbage family has been cultivated for many years and where 

 no known mode of infection is active. 



EXPERIMENTS ON PREVENTION BY THE REMOVAL 

 OF AFEECTED LEAVES. 



WHY UNDERTAKEN. 



Black rot being so destructive in New York in the season of 

 1898, there was an urgent demand from farmers for information 

 concerning methods of combating it; and it became imperative 

 that the Station should undertake some experiments on the treat- 

 ment of the disease. 



Both RusselH and Smith^ had suggested the removal of affected 

 leaves as being a promising line of treatment. They made some 



4 Russell, H. L. A Bacterial Rot of Cabbage and Allied Plants. Wis. Agr. 

 Exp. Sta. Bui, 6s : 38, 39. 



5 Smith, Erwin F. The Black Rot of the Cabbage. U. S. Dep't of Agr. 

 Farmers' Bui. 68 : 14. 



