310 BACTERIAL DISEASES OF PLANTS 



optimum temperatures. No growth could be obtained in the 

 plant or on agar or in bouillon at or above 29°C. (84°r.). 



The organism is rather long-lived on media but loses viru- 

 lence readily. It stains deeply with carbol fuchsin and by 

 amyl Gram. There is a feeble production of ammonia, indol and 

 hydrogen sulphide. A few cultures in litmus milk showed a 

 slight reduction of the litmus at the bottom. 



It is extremely sensitive to dry air and to sunlight. Four 

 minutes exposure to direct sunshine killed all organisms in the 

 insolated half of the thin-sown agar plates, exposed bottom 

 up on ice, although the colonies developed as usual on the covered 

 half of each plate. Taken from young, well-clouded bouillon 

 cultures, and dried in the dark at 22° to 25°C. on cover glasses 

 which were then dropped into suitable bouillon, the bacteria were 

 dead on 75 per cent of the covers in 24 hours, on 90 per cent in 

 48 hours, and on all at the end of 5 days. 



Technic. — The organism causing this disease grows readily 

 in +15 agar-poured plates when the temperature is under 29°C. 

 (not at all at or above this temperature)^ and there are no 

 difficulties in the way of isolation, other than surface con- 

 taminations, which are held in check, more or less, by short ex- 

 posures (20 to 30 seconds) in 1 :1000 mercuric chlorid water, 

 after which the spots are crushed in bouillon for the poured 

 plates. 



1 I felt so sceptical about 29°C. as the maximum temperature that in January, 

 1919, I asked Miss McCuUoch to do over for me this part of her work, which she 

 did with the following results: 



Tests of Bacterium maculicolum for maximum temperature. Isolations used: 



( Sanford, Florida, Col. 2 of April, 1916. 



J Floral Stalk, Col. 1, December, 1916. 



I Leaf, Col. 2, December, 1916. 



[ Mid-rib, Col. 6, March, 1917. 



I Ithaca, New York, Col. 3, November, 1918. 



I Greenhouse, Cols. 10, 11, 13 of January, 1919. 



(1) 18-25°C. 



All of the above isolations clouded +15 peptone beef bouillon moder- 

 ately in 16-18 hours. 



(2) 28.5-30°C. (Incubator heated by electricity and as workmen were chang- 



ing wires the current was sometimes off.) 

 "A" strains, which have been in artificial media from two to three 

 years, clouded slightly in 18 hours. 



