Mayi3, i9i8 SofTie BacteHal Diseases of Lettuce 387 



temperature six months in liquid media; stains readily with basic anilin dyes; is 

 Gram-negative; not acid-fast; not very sensitive to sodium chlorid (tolerates 6 -f per 

 cent); moderate toleration of acids and alkalies (tolerates oxalic to + 37 on 

 Fuller's scale; malic + 38; citric -f 37; tolerates sodium hydroxid in beef bouillon 

 to —30 Fuller's scale); is killed readily by drying; not very sensitive to stinlight; 

 retains its virulence for more than one year. 



CONTROL OF LETTUCE DISEASES 

 THE SOUTH CAROLINA AND VIRGINIA DISEASE 



So far as known, the Bacterium vitians gets into the field lettuce 

 only when it is in a weakened state owing to sudden cold weather which 

 is not cold enough to kill the plants. The treatment recommended is 

 the use of thoroughly decomposed green manure and well-seasoned stable 

 manure in which tissue-disintegrating bacteria have practically finished 

 their work. The bacteria then present in the soil are not active and the 

 plant, though weakened by sudden severe cold, may regain its stability 

 and be able to resist their entrance. 



The use of satisfactory windbreaks is obvious. 



THE KANSAS DISEASE 



As Bacterium marginale is a soil organism also, care should be taken 

 in watering the plants in the greenhouses that the roots only of lettuce 

 are watered. Soil should not be washed up nor spattered on the leaves. 

 Subirrigation is a safeguard. 



Good ventilation will almost, if not entirely, prevent the disease. 



SUMMARY 



Two new bacterial diseases of lettuce are described in this paper. 

 One occurred in South Carolina and in Virginia the same year both on 

 winter and late fall crops grown out of doors. The other is a disease of 

 greenhouse-grown plants in Kansas. 



The South Carolina disease occurred in the stems and roots and less 

 frequently on the leaves, following a sudden drop in temperature in 

 February. The Virginia disease occurred on the leaves only and fol- 

 lowed a heavy frost in October. An infectious organism identical with 

 the South Carolina bacterium was isolated. 



Inoculations were made with the bacterium isolated from the South 

 Carolina and Virginia lettuce, and this organism from both sources 

 proved to be infectious to both stem and leaves of lettuce. The name 

 "Bacterium vitians" is suggested for this organism. 



Besides this organism another was present in the Virginia lettuce^ 

 This was recognized as Bacterium viridilividum , an organism known previ- 

 ously to produce a lettuce disease. This colony also proved to be in- 

 fectious. 



