JOSEPH KRAFKA., JR. 



439 



According to this and the previous experiment, the reaction, 

 which determines the number of facets and whose rate is subject to 

 temperature modification, is initiated at 27° at or near the end of 3 

 days of development. Furthermore, it is practically over at the end 

 of 3f days, making the effective period of less than 18 hours duration. 



The actual time during which the reaction which determines the 

 number of facets takes place is doubtless much shorter than this for 





2 2% 3 



Dai|s at 27° 



3V4 3^2 d\ 4 



Fig. 12. Effect on the distribution and range in the Ultra-bar as a result of 

 subjecting successive bottles to 27° for 1, 2, 2f , 3, 3|, 3|, 3f , and 4 days, respec- 

 tively, before removal to 15° (see Table XVI). Broken line represents extension 

 of range in a second culture kept at 27° for 3 days. U. is the upper range of 

 27° stock counts; L., the lower range of 15° stock counts. 



the individual, since under the conditions of the experiment we are 

 deahng with material that may differ 12 hours in age. 



Initiation and Duration of the Effective Period at 15°. 



Experiment 62, of the same type as the preceding except that the 

 conditions were reversed, was carried out to determine when the 

 effective period was initiated at 15°. The same parents were used 

 as in Experiment 59. The cultures were made up at 27° and left 



