458 Journal of Agricultural Research vol. xx, no. 6 



The results show very clearly that Pseudomonas citri can remain viable 

 in the distilled water used for a period of eight days at temperatures 

 ranging from io° to 35 C. They suggest that the citrus-canker organism 

 under certain field conditions may remain viable in rain and surface water 

 for some time at a range of temperatures much larger than is usually 

 found in the field. 



Comparative tests with the organism in beef bouillon and in distilled 

 water at temperatures higher than 35 ° C. gave the same results. For 

 example, the thermal death point of the organism in the distilled water 

 was between 49 and 52 , just as in beef bouillon. 



CONCLUSIONS ON THE TEMPERATURE RELATIONS OF THE ORGANISM 



(1) The optimum temperature for the growth of Pseudomonas citri on 

 soluble starch agar, potato cylinders and in beef bouillon lies between 

 20 and 30 C. 



(2) There is a decided lag between the rate of growth at 15 C. and that 

 at 20 in all media. 



(3) The minimum temperature for the growth of Pseudomonas citri 

 is 5 C. on potato plugs. However, growth on soluble starch agar and 

 in beef bouillon is inhibited at this temperature, so that the minimum 

 temperature for the growth on these media must be slightly above 5 . 



(4) The maximum temperature for the growth of Pseudomonas citri 

 in beef bouillon is 43 C. for periods of less than 2 hours, 41 ° for a period 

 of 2 hours, 38 for a period of 24 hours, and 33 to 35 for periods longer 

 than 24 hours. Growth on potato cylinders and soluble starch agar 

 was, in all cases, inhibited at temperatures of 33 to 35 , so that the 

 maximum temperature for the growth on these media must be slightly 

 below 33 to 35 . 



(5) The thermal death point of the organism is above 49 and below 

 52° C. 



(6) The temperatures at which growth is inhibited must be clearly 

 distinguished from the temperatures at which the organism is killed. 

 This is especially important near the critical temperatures at or above 

 the maximum. The point at which growth is completely inhibited at 

 the higher temperatures is very sharp with a constant length of exposure. 



(7) The production of diastase by Pseudomonas citri on soluble starch 

 agar and potato cylinders follows the well-known chemical law of Van't 

 Hoff, between temperatures of 20 and 30 C. As in the growth of the 

 organism, there is a decided lag between the rate of enzym action at 15 

 and that at 20 . This fact has not been pointed out heretofore. Only 

 partial hydrolysis of the starch in the agar and the potato cylinders 

 occurs at 5 and again at 33 to 35 and 38 to 40 . 



(8) The citrus-canker organism is viable in ordinary distilled water 

 at temperatures ranging from io° to 35 C. for a period of eight days. 



