494 



AUSTIN RALPH MIDDLETON 



twenty-one days of culture without selection and twenty-three 

 days of mass culture. On December 7, sixty ex-conjugants 

 were isolated from the fast lines (ten from each of six diverse 

 lines), and sixty from the slow lines (twenty from each of two 

 slow lines, ten from each of two others). They were cultivated 

 in the way previously described. Balanced selection (i.e., in 

 effect no selection) was practised for fifteen days. Table 15 

 gives the numbers of generations produced by the fast and slow 

 lines during the five three-day periods of this experiment. No 

 lines were lost by death, and practically no selection of any 

 sort was necessary. 



The daily record sheets of this experiment show that during 

 its first five days the slow lines averaged more generations per 

 line than did the fast lines. Table 15 shows this for the first 



TABLE 15 



Experiment 3-C: Actual number of generations of the 60 fast lines of ex-conju- 

 gants and of the 60 slow lines of ex-conjugants during balanced selection for 15 

 days. The two members of each conjugating pair were individuals of the same 

 line 



