200 GENETICS AND EUGENICS 



Both Fi and F2 are intermediate in character in comparison 

 with the parent races, but F2 is shghtly more variable. Dif- 

 ferent lots of Fi progeny (combined in Table 30) give co- 

 efficients of variability of 8.29 and 6.88 respectively, whereas 

 F2 progeny have coefficients ranging from 9.66 to 11.77. The 

 extreme ranges of the parent races are not attained in F2. 

 This case is similar to that of weight inheritance in ducks, 

 except that F 2 is on the average less than Fi, being more 

 nearly intermediate between the parental races than was Fi. 

 The case is probably complicated by hybrid vigor in Fi, 

 which is not retained in F2. (See Chapter XXVII.) It is 

 evident that so many independent factors are involved that 

 no complete segregation occurs in F2. 



Table 31 shows the result of crossing two races of com (A 

 and B) differing in seed width. In this cross also, Fi, and F2 

 were alike intermediate, but the latter was slightly more 

 variable. It was found that the F2 plants differed in genetic 

 character as to seed width. An F2 with low seed width (143 

 mm.) produced an F3 likewise low (mean 141.3 mm.); and 

 F2 with seed width above the average (178 mm.) produced 

 an F3 of like character (mean 172.9 mm.). The range of the 

 low selected F3 extended even lower than the range of the 

 uncrossed low race (B), which is similar to the result obtained 

 by Punnett and Bailey in the weight inheritance of fowls and 

 suggests a similar explanation, recombination of factors. 



Some instructive cases involving multiple factors affecting 

 the size and shape of fruits have been studied by Gross. 

 See Fig. 132. It is evident that in these cases length and 

 width of the fruit are affected by numerous independent 

 factors which recombine so as to form a complete series of 

 intergrading forms. 



In garden peas the time between germination of the seed 

 and flowering varies greatly in different varieties. In early 

 varieties the time is short, in late varieties it is relatively long. 



Hoshino crossed two varieties of garden peas which had 

 been found to breed very true as to flowering time and flower 

 color. One variety was early and white flowered, the other 



