SELECTION WITHIN PURE LINES OF PESTALOZZIA 



169 



experiment. The variation of the strain during these generations may be 

 seen in table 7. 



The character selected in this study was length of spore. Spores of the 

 last culture shown in table 7 were mounted in agar on slides and measured. 

 The longest spore found was selected as the parent of a plus-selected line, 

 * and the shortest spore encountered was chosen as the parent of a minus- 

 selected line. When sporulation took place in the resultant cultures 

 the spores were measured and the mean spore lengths of the cultures 

 determined precisely as in experiments 1 and 2. Spores from each culture 

 were now mounted and measured, the longest found in the plus cul- 



TABLE 7 



Mean spore lengths of cultures of strain 17, grown prior to the selections in experiment 3. Mea- 

 surements in (JL. 



ture being selected to continue the plus line, and the shortest found in the 

 minus culture being taken as parent of the next generation of the minus 

 line. 



The selections thus begun were continued until ten had been made 

 when the experiment was discontinued. No attempt was made to make 

 the selections in the two lines at the same time. Thus the cultures in the 

 two groups usually developed under somewhat variable environmental 

 conditions so that a given selection is not precisely comparable with the 

 selection of the same number in the other line. However, in the long run 

 this variation is probably not significant since the fluctuations in environ- 

 ment should be about the same in summation for one line as for the other. 



GENETICS 7: Mr 1922 



