IX HEREDITY 165 



while a 3 "8 scattered from 3 "8 to 3 '3. Similarly, a 4-0 

 scattered from 3 "9 to 3 "2, and so on. On the data avail- 

 able it seemed clear that the parental forms could be 

 extracted and bred true, while the intermediate forms 

 represented new gametic combinations which broke up in 

 new ways, giving new forms. No large family having 

 been raised beyond F2 in this cross, we may examine 

 the data from another one. 



The AfifixTruitt cross had 2*8 and 4 "5 as the parental 

 values (Fig. 64). The figure 4"5 is uncertain, because there 

 was every indication that the American parent was 

 heterozygote in this respect. The Fj had 3' 6 loculi, and 

 the Fa spread from 2"9 to 4*8. Only five F3 families 

 were raised ; one of these was derived from a 3*3 plant, 

 and its twenty-one off'spring ranged from 2 '9 to 3 "4, thus 

 resembling the Egyptian parent closely but not exactly. 

 Another 3 '3 behaved in the same way, and repeated this 

 behaviour in F4. Conversely, a 4 "8 gave only 4 '6 to 

 4'9 ; while a 4"5 gave 4*2 to 4'6. The offspring of a 

 4"3 form broke up into a wide scatter from 3 "3 to 4"9 ; 

 several small families of these were bred on into F^, but 

 the largest and most interesting was one from a 4 "5 

 plant, which consisted of twenty-nine plants, ranging only 

 from 4*5 to 5*0, and giving a frequency polygon with the 

 same probable error as the parent. 



The inter-Egyptian cross was expected to unravel a 

 portion of this tangle, but although the critical numbers 

 were doubled, and the data classified to half-grades the 

 result was much the same (Fig. 65). Sultani (3'20) 

 crossed by Afifi (2-80) gave an Fi at 3-00. The Fj of 

 this broke up with great symmetry over the parental 

 extremes with a single mode at the Fj value. The 

 spread of this curve of the F2 is too narrow to be the 

 expression of a 1:2:1 ratio, so it is probable that at 

 least two factors are involved even here. There is a slight 

 indication of the possible nature of these factors, namely, 



