166 



CARL DOWNEY LA RUE 



apparently been so nicely balanced by one where the minus line has grown 

 longer and the plus line shorter, that the result has been an almost absolute 

 identity of the two lines as regards length of spore appendages. 



TABLE 6 



Mean appendage lengths of generations of experiment 2. Each mean was computed from the 

 means of the cultures in its group for that generation. Each mean, except in the intermediate group, 

 is based on approximately 1000 measurements. Measurements are given in JJL. 



Difference between plus-selected line and minus-selected line =0.171 +0.1 15. 

 Difference between plus-selected line and unselected intermediate line = 0.108 0.242. 

 Difference between minus-selected line and unselected intermediate line =0.279 +0.239. 



The minute scrutiny of each generation in the course of this experiment 

 and of experiment 1 made it possible to detect at once the appearance of 

 any aberrant form by mutation. It is desirable that such control be kept 



