204 Journal of Agricultural Research voi. xv.no.s 



pletely, which required nearly two months, an abundant growth of the 

 organisms had been made. On November 8, 191 6, the dry remains of 

 the agar, carbonate, etc., from three of the tubes were transferred to 

 tubes of bouillon. Growth occurred in all three tubes thus inoculated, 

 and in each case the identity of the organism was established by inoculat- 

 ing cucumber plants. Two of the remaining three tubes were similarly 

 tested on February 9, 191 7. Growth resulted i;i each case, and inocula- 

 tions again proved that the clouding of the bouillon was due to the 

 angular-leafspot organism. Since all other evidence is opposed to the 

 possibility of the formation of spores, the writer is inclined to explain 

 the survival of some of the bacteria in these tubes by assuming that they 

 were protected from complete desiccation. 



THERMAL RELATIONS 



The thermal death point of the angular-leafspot bacterium is be- 

 tween 49° and 50° C. Tests were made in lo-cc. portions of beef bouillon 

 in 'thin-walled test tubes at 46°, 48°, 49°, 50°, 52°, and 55°. Ten min- 

 utes' exposure at 46° must have killed a large proportion of the organ- 

 isms, because growth in tubes so exposed was much slower in appearing 

 than in the unheated controls. In each test some but not all of the tubes 

 exposed at 49° C. showed no growth. In none of the tests did growth 

 occur in tubes exposed at 50° or temperatures above that point. 



An interesting contrast between the relation of temperature to 

 angular-leafspot and its relation to the bacterial-wilt of cucumber was 

 brought out at Madison, Wis., in 191 6. The maximum temperature as 

 recorded by the United States Weather Bureau there averaged 36.7° C. 

 (98° F.) for the five days July 26 to 30, inclusive. The highest tempera- 

 ture at the Weather Bureau Observatory was 38.3° C. (101° F.), but in 

 direct sunlight and near the ground undoubtedly the temperature was 

 higher. This unusually hot weather did not appreciably check the devel- 

 opment of angular-leafspot, which reached its maximum development 

 within about 10 days thereafter, but it practically stamped out the bac- 

 terial-wilt. Smith {14, p. 2og) accounts for the bacterial-wilt having 

 been found only in cool climates on the basis of the low thermal death 

 point, 43° C, of the causal organism. 



The relation of temperature to growth in artificial media has been 

 found to agree with the report of Smith and Bryan {15, p. 470), and so 

 need not be given in detail. 



The sensitiveness of the bacteria to freezing was tested by exposing 

 them in different media in glass test tubes outside a north window during a 

 period of low temperatures in the winter of 1 91 6-1 7. Dilute suspensions 

 of the bacteria in distilled water, freshly -inoculated tubes of beef bouillon, 

 beef bouillon with approximately 2 per cent of sodium chlorid, and 24- 

 hour agar slope cultures were exposed. During the first 9 days of the 



