SEED COAT COLOR IN GARDEN BEANS. 



75 



mottling. In later generations black beans predominate, with some 

 signs of indistinct mottling in some cases. The occasional appearance of 

 mottling suggests that one or both raottUng factors are carried by Crease- 

 back. The fact that mottling appears with Blue Pod Butter which in 

 all other crosses seems to carry the Y only, and with Challenge Black 

 Wax which carries the Z, indicates that Creaseback must carry both 

 Y and Z, or that more than one strain has been used. If coupled factors 

 are present there should appear beans breeding true to the mottled 

 character. No such cases have been clearly shown. If we assume that 

 the appearance of solid or nearly solid black beans is due to the presence 

 of an additional factor X, which renders the black color epistatic to 

 mottling, we have a hypothesis that is fairly well supported by the limited 

 data available. These data are shown in Table VI. Crosses 31 and 32 



Table VI. — Crosses involving Creaseback. 



were among the earlier crosses made, and while no individual records of 

 mottled beans in r2 were kept, it is evident that mottling did occur, but 

 it was very faint and nearly obscured by black in most cases. There 

 were a few dark mottled beans, however, and one of these being selfed 

 gave the proportions of mottled, self-colored and white beans shown in 

 the table. In crosses 31 and 32, Table VI., Creaseback may have the 

 formula yZ, for in this case, assuming the presence of X in Creaseback 



