SELECTION WITHIN PURE LINES OF PESTALOZZIA 



159 



change is effected. The intermediate line shows continual fluctuation 

 from generation to generation. Similar fluctuation has been found by 

 all workers who have made careful studies of variation in pure lines of 

 organisms. It is presumably due to environmental influences, although 

 the writer was unable to correlate very considerable fluctuations in the 



FIGURE 4. Graph of the mean spore lengths of parent cultures of experiment 1. P repre- 

 sents the parents of the plus-selected line, M those of the minus-selected line, and I, those of the 

 unselected intermediate line. The ordinates are lengths in n; the abscissae, the generations of 

 the experiment. 



spore length of Pestalozzia with any significant fluctuations in any of the 

 environmental factors which are easily measured. The fluctuations in 

 the plus and minus selections appear to be due, not to selection, but to 

 such influences as cause the variations in the unselected intermediate line. 

 In most cases the fluctuations of the plus and the minus selections in a 



GENETICS 7: Mr 1922 



