POTATO-SCAB. 537 



Potato-Scab. 



The symptoms of this common disease consist in the formation 

 of areas of dry corky, tissue on the surface of the tubers. 

 These soon fall a prey to bacterial forms, and rotting takes 

 place, soon, however, to be cut off from the healthy tissue by 

 a layer of cork. The disease continues to spread deeper into the 

 tuber, till the reserve materials are used up or rendered useless. 

 BoUey ^ ascribes the disease to a particular Bacterium which he 

 isolated and used to carry out infections on healthy tubers. 

 "Without doubt this Bacterium is common in tubers exhibiting 

 " scab," but other conditions may have caused the disease in the 

 first instance. 



Thaxter^ believes that the scab-disease of both potato and 

 beetroot is. caused by a fungus Oospora scabies (p. 497). 



Schilberszky ^ in investigating a potato-scab, found a fungus 

 which he places amongst the Chytridiaceae ; its life-history has 

 not as yet been followed out. 



Bacterial Diseases of Beetroot. 



Beetroot and sugar beet have shown themselves very liable 

 to diseases which have been ascribed to bacterial agency. Thus 

 in sugar beet which yielded a low proportion of sugar, Arthur and 

 Golden * found the cells inhabited by a multitude of bacteria. 

 These inhabited both roots and leaves, without, however, giving 

 any external evidence of their presence. 



Hiltner^ observed that beetroot died in cousequence of loss 

 of its root-hairs. This loss was traced to bacteria, and, after 

 these had been killed by disinfection, the same roots again 

 produced normal root- hairs and grew well. 



More recently Sorauer ^ describes a disease of these crops 

 in Germany. The lower ends of the plants become black, while 

 from the undiseased portions of the surface there exuded a 

 gummy fluid containing bacteria, yeasts, and fungi. He considers 



' BoUey, "Potato-Scab.'' Agricvltiircd Science, 1890. 

 ^Thaxter, Reports of the Connecticut Agric. Exper. Station, 1890 and 1S91. 

 ^ Schilberszky, Vorlauf. Mittheilung, Ber. d. deutsch. hotan. Ges., 1896, p. .36. 

 ^ " Diseases of the Sugar Beetroot. " Indiana Agric. Exper. Station, Bull. 39,1892. 

 ■' Hiltuer, Sach-Hsch. landwirth. Zeitung, 1894. 



^ Blatter f. Zuckerriibenbau, 1894; also Centralblatt f. Bakteriologie und Para- 

 -sitenkiinde, xviri. , 189.5, p. 2!I5. 



