No. 530] COEFFICIENT OF INDIVIDUAL PREPOTENCY 473 



II. The Measurement of Individual Prepotency 



However well one may know the somatic characters of 

 an individual or however intimate his knowledge of its 

 ancestry the ultimate test of its value as a starting point 

 for a new race is the quality of its offspring. The proof 

 of the parent is its produce has been recognized as valid 

 by various breeders since the time of Louis Vilmorin, who 

 separated the parent beets and judged them individually 

 by their offspring. The " ear-to-row " test in corn breed- 

 ing, Petkus von Loehow's row-tests in rye and Hays's 

 "centgener power" all represent attempts by practical 

 breeders to obtain measures of individual prepotency as 

 the term is used here. Galton's study of the distribution 

 of prepotency in horses falls in the same class. 



The method of estimating prepotency directly from the 

 mean value (e. g., sugar content) of the offspring, or 

 from the number of offspring surpassing a given stand- 

 ard (e. g., a mile in 2 :30, or better, on the track) has dis- 

 advantages which will be obvious to those acquainted 

 with elementary statistics. 



So far as I am aware the credit of first recognizing the 

 need of taking into account both type and variability in 

 the criterion by which the relative desirability of the indi- 

 vidual parents should be judged is due to Waugh. 



In discussing some results secured on experiments with 

 peas he remarks : 4 



. . . There were, as always, some exceptional cases of individual 

 vines which showed a marked* ability to transmit their individual char- 

 acters to their oflfeprijig. The selection of such prepotent plants is 

 evidently an important matter in plant breeding-. In order to exhibit 

 this difference we have computed a coefficient of heredity for each 



Waugh 's formula is 



C = 1/VD, 



where 



C = coefficient of individual heredity, 

 a — standard deviation of offspring, 



4 Ann. Eept. Mass. Ag. Exp. Sta., Vol. 21, p. 172, 1909. 



