1909.] PUBLIC DOCUMENT — No. 31. 171 



Studies in Heredity. 



From the beginning of this experiment careful studies in 

 heredity have been phuined. As this year's report covers only 

 the second generation of peas no very conclusive results could 

 be expected. It must be confessed, however, that the figures for 

 this year not only lack conclusiveness but they are decidedly con- 

 fusing. It was to be expected, of course, that the progeny of 

 prolific vines would be more prolific than those from unprolific 

 vines, and that plants which in 1907 gave a large number of 

 peas per pod would yield progeny in 1908 with relatively large 

 nund)ers of peas per pod. As a matter of record, this reasonable 

 expectation of heredity was not fulfilled to a degree which 

 would satisfy any practical plant breeder. 



The measure of heredity is best computed by the methods 

 introduced by Galton, and improved by Pearson in England, 

 and now used largely among scientific plant breeders in America. 

 This method involves somewhat complicated mathematics, which 

 we need not take up here.^ It will be sufficient if we explain 

 that absolutely perfect inheritance (which never occurs) would 

 be represented by the integer 1, and that various degrees of 

 heredity would be measured by decimal fractions or percentages 

 running down from 1 to 0. It may be said, further, that careful 

 studies of most subjects where heredity is known to operate nor- 

 mally show coefficients varying from .15 to .52 or .53, but a 

 coefficient as large as .50 seems to be rare. In human beings, 

 for example, heredity seems to run at about .30. Certain com- 

 putations will even show slightly negative results ; })ut unless 

 the figures are large, such negative coefficients indicate only 

 that heredity has been practically o])literated with respect to the 

 individuals and the characters under examination. 



The coefficients of heredity shown in the pea progeny of 1908 

 were as follows : — 



Coefficients of Heredity. 

 Length of vine, ...... -\- .IIQ 



Pods per vine, ...... -f-.158 



Peas per pod, ......_ .083 



Total peas per vine, ..... -|- .035 



> Any one wishing to studj- this method of measuring hcreditj- maj- consult E. Daven- 

 port's Principles of Breeding, p. 4S6. 



