APPENDIX C. 



225 



EXPERIMENTS ON SWEET PEAS BEARING ON THE LAW OP REGRESSION. 



The reason why Sweet Peas were chosen, and the methods of 

 selecting and planting them are described in Chapter VI., p. 79. The 

 following Table justifies their selection by the convenient and accu- 

 rate method of weighing, as equivalent to that of measuring them. 

 It will be seen that within the limits of observed variation a 

 difference of 0T72 grain in weight corresponds closely to an average 

 difference of 0"01 inch in diameter. 



Table 1. 



Comparison of Weights of Sweet Peas with their Diameters. 



Distinguishing 

 letter of 



"Weight of one 

 seed in grains. 



Length of row of 

 100 seeds in 



Diameter of one 



seed in hundredths 



of inch. 



seed. 



Common difference 

 = 0-172 grain. 



inches. 



Common difference 

 = 01 inch. 



K 



1-750 



21-0 



21 



L 



1-578 



20-2 



20 



M 



1-406 



19-2 



19 



N 



1-234 



17-9 



18 







1-062 



17-0 



17 



P 



•890 



16-1 



16 



Q 



•718 



15-2 



15 



The results of the experiment are given in Table 2 ; its first and 

 last columns are those that especially interest us ; the remaining 

 columns showing how these two were obtained. 



It will be seen that for each increase of one unit on the part of 

 the parent seed, there is a mean increase of only one-third of a unit 

 in the filial seed ; and again that the mean filial seed resembles the 

 parental when the latter is about 15*5 hundredths of an inch in 

 diameter. Taking 15 5 as the point towards which Filial Regression 

 points, whatever may be the parental deviation from that point, the 

 mean Filial Deviation will be in the same direction, but only one- 

 third as much. 



