No. 549] ON DIFFERENTIAL MORTALITY 521 



of the differences between the general and the viable 

 samples. Here the different comparisons are shown from 

 left to right in the order in which they are given from 

 top to bottom in Table Y. The distances of the solid dots 

 below the zero bar indicate the amount of the negative 

 deviations, the circles above the positive deviations. 



From all of these considerations, we conclude that 

 seeds which produce fertile plants are on the average 

 neither lighter nor heavier than random samples of the 

 population. 



While the results for the means furnish no evidence 

 for a selective mortality, the standard deviations are very 

 suggestive of its existence. In 19 cases, the S.D. of the 

 seeds which produce fertile plants is lower than that of 

 the series from which they were drawn, while in 9 cases 

 it is larger. The deviation from the equality to be ex- 

 pected if the differences were due purely to an infinite 

 number of random sampling is therefore 



5 ±. 67449 V.5 X-5 X 28 = 5 ± 1.79, 



which is perhaps statistically significant. The chances 

 against the result being due to the errors of sampling are 

 roughly the same as those against 19 heads and 9 tails, or 

 vice versa, in coin tossing. 



Not only the inequality of the divisions of the signs 

 into positive and negative, but the magnitude of the 

 deviations themselves evidence for a selective mortality 

 which reduces variability without sensibly affecting the 



19 negative — .122 ; the whole 28, — .071. The far greater 

 magnitude of the negative deviations is made clear by the 

 generally greater lengths of the bars below the zero line 

 in diagram 2. Considering the individual differences in 

 their relation to their probable errors, we note that in 7 

 cases the difference is over 2.5 times its probable error. 

 All of these are negative in sign. 



The coefficient of variation, that is, 100<r/ m, should show 

 most clearly whether both larger and smaller seeds fail 



