278 IJACTERIAL DISEASES OF PLANTS 



darkens rapidly on exposure to air more resistant to this disease 

 than those which possess this property to a feeble degree? Are 

 those varieties whose lenticels open freely in wet soil specially 

 subject to this rot? I believe they are. 



Transmission. — In two localities Appel saw this disease 

 develop severely in places where potato refuse from rotten pits 

 had been thrown out (for reference to a similar observation on 

 black rot of the cabbage see No. II) and in one of these places 

 the soil was still infectious after 5 years (Appel I.e., p. 387). 

 Appel also found that sound-looking tubers from diseased fields 

 often carried the infectious organism on their surface. Should 

 rotting potatoes be left in the field? Should they be thrown on 

 the dung heap, or fed to stock? What do you conclude respect- 

 ing selection and treatment of seed tubers? What respecting 

 early digging of the tubers, i.e., before fall rains have set in? 

 What respecting the necessity for dnj and eool storage, especially 

 in years when the rot is very prevalent? 



The organism is sensitive to dry air and for this reason pota- 

 toes should be dry when stored to avoid further rot in pits and 

 cellars. 



Mr. Melhus states that he has combated this disease in the 

 field very successfully by persistently pulling out the diseased 

 hills and exposing them to the light and air (oral communi- 

 cation). 



My own experiments lead me to believe that well-drained 

 fields should be much less liable to attacks of the tuber rot in 

 autumn than those which become water-logged following heavy 

 rains. 



Rot due to Bacillus phytophthorus ceases at 4°C. and below 

 8°C. (46°F.) it is slow. Potato tubers from fields where this rot 

 has prevailed should therefore be stored at low temperatures 

 and disposed of early. 



LITERATURE 



Consult Appel's paper ''Untersuchungen uber Schwarzbein- 

 igkeit und die durch Bakterien hervorgerufene Knollenfaule der 

 Kartoffel" in Arbeiten aus der Biol. Abth. f. Land.-u. Forst- 

 wirthschaft am Kaiserl. Gesundheitsamte, Band III, Heft 4, 



