Neo-Mendelism 77 



may be referred to as 1:4:6:4:1. When three cumula- 

 tive factors are considered the F2 ratio would become 

 1:6:15:20:15:6:1 (see fig. 16), that is, one of each 

 of the original parents out of 64 individuals. In the 

 same way the six cumulative factors assumed, which 

 is really a conservative number, would give the following 

 F2 ratio: 1:12:66:220:495:792:924:792:495:220:66: 

 12:1, that is, one of each of the original parent types 

 out of 4096 individuals of the F2 generation. 



With these facts it is easy to explain the experience of 

 breeders and horticulturists. In the first place, practi- 

 cal breeders are not as carefully discriminating as are 

 geneticists, so that they would put their individuals of 

 Mirabilis into three classes, that is, red, pink, and white, 

 without considering the various degrees of redness or 

 pinkness. Therefore if they were dealing with six 

 cumulative factors and grew less than 4096 individuals 

 of the F2 generation, the chances are that they would 

 obtain no individuals representing either the red parent 

 or the white parent. Naturally they would conclude 

 that the original cross produced an intermediate hybrid, 

 which when inbred without exception bred true to the 

 intermediate hybrid character. The question might be 

 raised in reference to the later generations. Would not 

 the original parent type reappear in some generation 

 later than F^ ? The mathematics of the situation is too 

 complex for presentation, but the result can be visuahzed 

 in a less exact way. It has been seen that the vast 

 majority of the F^ are intermediates of varying degrees, 

 that is, when the Fi intermediates were inbred the result- 

 ing F2 was made up of practically all intermediates and 

 no extremes. Inbreeding F^, therefore, would continue 



