I30 



Journal of Agricultural Research 



Vol. IV. No. a 







30X! 



2SV 



zov 



/S'C 



/crc 



in the usual way. Beef-extract agar, without salt/ was found to be 

 the most satisfactory medium for the purpose. 



Immediately after the hanging-block cultures were made, the sUdes 

 bearing them were placed in incubators running at the requisite tempera- 

 tures. They were not removed therefrom except for a short time at the 

 close of each hour for examination with the microscope. To avoid 

 inaccuracies, due to possible variations in temperature in different parts 

 of the incubator chambers, care was taken to see that the temperatures 

 recorded were those in the immediate vicinity of the preparations 



studied. 



THERMAL EFFECT ON GERMINATION 



The maximum temperature for growth is apparently a little below 

 41° C, although occasionally slight evidence of the beginning of germina- 

 tion of gonidia was ob- 

 served at this point. 

 Germination was most 

 rapid between 35° and 

 40.5°, and little or no 

 differences were noted 

 in various trials be- 

 tween these limits. 

 At the temperatures 

 mentioned the first 

 evidence of growth 

 was observed at the 

 end of three hours, and 

 below this the time 

 gradually increases: 5 

 hours are necessary at 

 30°, 8 hours at 25°, 11 hours at 20°, 18 hours at 15°, and 2 days at 10° C. 

 (fig. i). The largest percentage of germination is usually secured at from 

 30° to 37° C. Unevenness in germination is evident at 25°, and from this 

 point down it becomes more and more apparent until it is especially pro- 

 nounced at 10° C. Plate XV, figures i and 2, illustrates the character- 

 istic appearance of the germinating gonidia at 35° C. 



No attempt was made to determine the exact minimum temperature 

 for germination, but some previous unpublished studies of the writer 

 indicate that it lies somewhere near 5° C. Twenty test-tube cultures, 

 ten in beef broth and ten on potato cylinders, immediately after inocula- 

 tion with material containing gonidia were placed in a refrigerator where 

 the temperature varied from 5° to 7° C. Only a little growth was noted 



Fig. I.— Chart showing the relation of temperature to time of germi- 

 nation. 



• A modification of the formula given by F. D. Chester. 

 Bacteriology, p. 28. New York, 1901.) 



(Chester, F. D. Manuad of Determinative 



