POTATO STEM DISEASES. l7 



Continent, but while in England Dr. M. C. Cooke sent specimens, as 

 did also Dr. John Wilson, from Scotland. It is regarded as capable of 

 causing much harm, but fortunately has not as yet become common. 



POTATO STEM DISEASES. 



BLACKLEG. 



" Schwarzbeinigkeit,''' or blackleg, is a name applied to a disease 

 seen commonl}^ in central Europe. It is characterized by the black- 

 ening and rotting of the main stem, accompanied })y a checking of the 

 growth, uprolling, yellowing, and ultimate death of the leaves, and 

 more or less rotting of the tubers. It has been exhaustively studied 

 in recent years by Appel" in Gerniany, who concludes that it is due to 

 bacteria {Bacillus pliytophthorus^ and perhaps other allied species), 

 which either enter from the soil or are carried in the seed tuber. 

 These start the disease below ground, the rot proceeding, as a rule, 

 from the seed tuber to the 3'oung plant. Appel's conclusions are gen- 

 erally accepted by pathologists in Germany, Holland, and Belgium, 

 and, so far as learned, in England. 



The writer had opportunity to see rnuch of the German disease in 

 the vicinity of Berlin, and to verifv Doctor AppeFs observations, in a 

 measure, in his own laboratoiy. Later (August) the same malady was 

 seen in England, where it is said to be common, though apparently 

 less troublesome than Appel reports it from Germany. All of the 

 personal observations of the writer therefore lead to an indorsement 

 of AppeFs conclusions both as to the bacterial nature of the disease 

 and as to its widespread occurrence and economic importance. 



In France a similar if not identical disease is attributed to bacteria. 

 Delacroix, who has studied this, considers the organism causing the 

 disease, which he calls Bacillus solanicola, to be specifically distinct 

 from that described by Appel. He kindlj- showed the writer speci- 

 mens of the French disease in his garden in Paris, but it was in a 

 stage so much more advanced than that seen in Berlin that a comparison 

 of the two does not seem justifiable. 



Of course, the possible occurrence of these stem diseases in America 

 was kept in mind. The writer has never seen much, if any, of the 

 same trouble in potato fields in the Mortheastern States and adjacent 

 Canada which have come under his observation. Certainly it is not so 

 common in America as it is in Europe. The S3nnptoms correspond, 

 however, somewhat closely to certain diseases attributed to Rhizocto- 

 nia in the South and West.^ 



« Appel, O., Arb. aus Biol. Abt. Gesundheitsamte, 3: 364 (1903). 

 & See especially Selby, A. D., Ohio Exp. Sta. Buls. 13i> aiiJ 145, and Rolfs, F. M., 

 Colo. Exp. Sta. Bills. 70 and 91. 



8838— >;o. 87—05 3 



