460 



AUSTIN EALPH MIDDLETON 



replaced by a reversed difference. The experiment with bal- 

 anced and reversed selection is that described next. 



Experiment 1-A Balanced selection and reversed selection, 

 December 4 to December 23, 1913. 



This experiment was undertaken to test by the methods set 

 forth above whether the difference in fission rate shown at the 

 end of thirty days of opposite selection by the two sets of lines 

 in Experiment 1, part 1, were hereditary. In the first place 

 fifty of the slow lines and fifty of the fast lines were subjected 



TABLE 2 



Experiment 1-A: Actual number of generations per ten lines per ten-day period 

 for the 50 fast and 50 slow lines of Experiment 1, Part 1, when subjected to bal- 

 anced selection 



to balanced selection for twenty days. Table 2 gives the actual 

 number of generations that these fifty fast and slow lines pro- 

 duced. The sets are divided into groups of ten lines each. 



The average difference of fission rate per line per day for the 

 whole thirty days of Experiment 1, part 1, while selection was 

 in progress was 0.267 generation in favor of the fast lines. For 

 the twenty days of balanced selection it was 0.037 generation. 

 This would seem to indicate that the direct selection of Experi- 

 ment 1, part 1, had produced a very slight heritable difference 

 in fission rate between the two sets, especially since the differ- 

 ence 0.05 generation of the second ten-day period of balanced 



