POTATO-^^CAB. 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. 

 IJolley ^ ascribes the disease to a particular Bacterium which he 

 isolated and used to carry out infections on healthy tubers. 

 Without doubt this Badcrivm is common in tubers exhibiting 

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

 tirst instance. 



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

 beetroot is caused Ijy 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 liabh^ 

 to diseases which have been ascribed to bacterial agency. Thus 

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

 (jolden-* 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 consequence of loss 

 of its root-hairs. Tlii.s 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 



' Hoi ley, "Potato-Scab." A<jri<-nltHral Srknce, 1S90. 



-Thaxter, H< ifortt of thi' Conuvtirut A'jrk. t'xjxr. Statin)), 1890 and 1S91. 

 ■'Schilberszky, Vorlauf. Mittheilung, Bn: d. fle)it^ih. hotm). (Uj*., ISliG, p. ."JO. 

 ^ " Diseasesof the Sugar Beetroot." IniJiaiia A-jric. Eip'r. S/ntioii, Bull. :V.). 1H92. 

 '■Hiltner, Siichsi-irh. kuxluirth. Zfittuxj, 1S94. 



'^ B/atte)- /. Zttckff)-iih<')il,ft)i, 1894; also C^^ti-alhlatt /. /iftkt^riolonie nml /'nrn- 

 .■iittnkimde, xviii., ISO.i. p. -iilo. 



