THE BLACK ROT OF CRUCIFERS : TRANSMISSION 159 



Transmission. — Greenhouse slugs may be used, feeding them 

 first on infected leaves and then on sound plants. Also larvae 

 of the cabbage butterfly. Can the disease be spread by aphides? 

 If opportunity exists, collect seeds from diseased plants and 

 try to isolate the organism from them (rather difficult) and to 

 get infected seedUngs from them. Why should a seedsman 

 collect and disseminate seeds from stock he knows to be diseased? 



The writer has seen a serious outbreak of the disease on 

 parts of a cabbage field that received as a manure the diseased 

 refuse from a storehouse in which brown-rotted cabbage had been 

 wintered over (see No. VII). He has seen an entire crop ruined 

 and the organism introduced into the soil of a field previously 

 free from it by setting it out with plants from an infected seed 

 bed. (See U. S. Dept. of Agr., Farmers' Bull. No. 68.) 



MEANS OF PREVENTION 



Use of seed derived from healthy plants. Seed beds on 

 land free from the disease. Care in transplanting that roots 

 shall be wounded as little as possible. 



LITERATURE 



For literature, etc., consult: Black rot of Cruciferous Plants 

 in ''Bacteria in Relation to Plant Diseases," Vol II, pp. 300-334, 

 Carnegie Institution of Washington, 1911. See also Ibid., 

 Vol. I, Figs. 4, 5, 6, 7, 18, 19, 76, 77, 78, 79, 87, 115, 116, 117. 



The first important paper on the subject was published 

 in 1893 by Prof. L. H. Pammel (Bot. Gaz., Jan., 1893). The 

 organism was first named Bacillus campestris by Pammel in 

 1895 in Bull. No. 27, Iowa Agr. Col. Exp. Station, pp. 130-134. 



The last paper is by Walker and Tisdale: Observations on* 

 Seed Transmission of the Cabbage Black Rot Organism. Phyto- 

 pathology, Vol. 10, No. 3, March, 1920, pp. 175-177. 



These authors have proved introduction of the disease into Wisconsin on seed 

 imported from north Europe. They have also established that the disease can 

 be reduced to negligible proportions by soaking the seed for 30 minutes in 1-1000 

 mercuric chlorid water. 



