LAW OF EECOMBINATION. 21 



results; for instance, W Nc X WnC £ind WNC X Wnc both give 

 WWNnCc. There are, however, twenty-seven different combina- 

 tions amongst the sixty-four matings; these, together with the 

 number of matings in which each occurs, are shown in Table 11. 



Table II. — The twenty-seven different types in the second generation of a hybrid between 

 a ivinter wheat, W, with weak straw, n (absence of nonlodging character), and open chaff 

 c (absence of closed chaff), and a spring wheat, w (absence of winter character), with stiff 

 straiu, N (nonlodging) , and closed chaff , C. 



Serial 



Propor- 



Formulse of 



Serial 



Propor- 



Formulse of 



Serial 



Propor- 



Formulae of 



No. 



tions. 



the types. 



No. 



tions. 



the types. 



No. 



tions. 



the types. 



1 



1 



WWNNCC 



10 



2 



WwNNCC 



19 



1 



wwNNCC 



2 



2 



WWNNCc 



11 



4 



WwNNCc 



20 



2 



wwNNCc 



3 



1 



WWNNcc 



12 



2 



WwNNcc 



21 



1 



WW NNcc 



4 



2 



WWNnCC 



13 



4 



WwNnCC 



22 



2 



wwNnCC 



5 



4 



WWNnCc 



14 



8 



WwNnCc 



23 



4 



WW Nn Cc 



6 



2 



WWNncc 



15 



4 



WwNncc 



24 



2 



WW Nncc 



7 



1 



WWnnCC 



16 



2 



WwnnCC 



25 



1 



wwnnCC 



8 



2 



WWnnCc 



17 



4 



Wwnn Cc 



26 



2 



wwnn Cc 



9 



1 



WWnncc 



18 



2 



Wwnncc 



27 



1 



wwnncc 





16 







32 







16 





16+324-16=64. 



Types Nos. 1, 3, 7, 9, 19, 21, 25, and 27 are homozygote, and will all reproduce true to seed. Type No. 1 

 was the type sought in this cross. 



The first nine of these twenty-seven types, constituting one-fourth 

 of the whole generation, are pure winter wheat ( TFTF), the next 

 nine (Nos. 10-18), constituting one-half of the generation, are hybrids 

 between winter and spring (Ww), while the last nine, constituting 

 one-fourth, are pure spring wheats (ww). Each of these three 

 groups of nine types is subdivided in like manner into one-fourth 

 pure nonlodging, one-half hybrid between lodging and nonlodging, 

 and one-fourth pure lodging. Thus, the first three types are all pure 

 winter and pure nonlodging; these three types constitute 4 sixty- 

 fourths of the generation, or one-fourth of the first group of nine. 

 The second group of three are all pure winter, but- hybrid with 

 reference to the lodging character; these three constitute 8 sixty- 

 fourths of the generation, or one-half of the first group of nine, etc. 

 Thus, each of the three groups based on the winter-spring character 

 pair is subdivided into three groups based on the straw character, 

 thus giving nine groups based on these two character pairs. Each 

 of these nine is similarly divided into three t5rpes, based on chaff 

 character. This gives in all twenty-seven different combinations. 

 Of these twenty-seven combinations, eight are seen to be homozy- 

 gote with reference to all three character pairs. This means that 

 these eight are pure bred as far as these characters are concerned 

 and will show these characters in all their progeny. The other nine- 

 teen types are heterozygote, or cross-bred, with reference to one or 

 more of the character pairs, and will thus not reproduce true to seed. 



165 



