AN ANALYSIS OF THE EFFECT OF SELECTION. 



11 



to weight the results from different parents according to the number 

 (and therefore reUabiUty) of their offspring. In the present case, 

 also, it gives an extremely large probable error, and probably gives a 

 less accurate value for the coefficient itself. The usual method has 

 accordingly been followed, but little reliance is to be placed on the 

 biological significance of the results obtained. Hence in the follow- 

 ing discussion the correlation coefficients will be largely ignored. 



Fig. 3.— Means and standard deviations for 864 inbred plus line. The gener- 

 ation number is given on the abscissa; bristle number on the ordinate. 

 The dotted lines represent reverse selection. 



The values for M and a in the 864 line are plotted in figure 3. 

 Selection has apparently affected this line hardly at all. This is per- 

 haps because in the early generations so few individuals were bred 

 from. Reversed selection (dotted line in curve) was ineffective in 

 the eleventh to thirteenth generations, thus indicating again that at 

 that stage at least the line was not capable of modification through 

 selection.^ 



1002 Line. 



The second inbred plus line is descended from culture 1002. The 

 female in this culture was of the constitution — tt" and the four 

 males were from the peach, spineless, kidney, sooty, rough stock. 



'The fact that the signs of the differences between the means are reversed when selection is 

 reversed is due simply to the fact that the parents selected are now below the mean of the line, 

 instead of above it. The difference between the means, like the correlation coefficient, is of 

 slight significance when the number of parent individuals is as small as in these experiments, and 

 for the same reasons. 



