70 



MASS, EXPERIMENT STATION BULLETIN 185. 



In cross 54, Mohawk X Burpee Stringless, in the F3 and F4 genera- 

 tions, 54 plants yielded only mottled beans. This is explained by the 

 fact that only two parent plants were involved, and both happened to be 

 homozygous for mottling. 



In Table III. are shown the results obtained from crosses of mottled 

 and white varieties. In all such crosses the Fi beans have been mottled,, 

 and all extracted whites have bred true. Extracted self-colored beans 

 have sometimes bred true and sometimes yielded self-colored and white 

 in approximately a 3:1 ratio, never mottled beans. As shown in the 

 table, the usual result in F2 seems to be a 9:3:4 proportion. 



Table III. — Crosses of Mottled with White Beans. 



Cross 141, Davis Wax X Keeney Rustless, yielded no self-colored 

 beans. It will be shown later that Davis carries the coupled factors YZ, 

 and as soon as pigment is introduced yields mottled beans. This being 

 true, and Keeney Rustless also bearing YZ, no self-colored beans can 

 appear. In cross 309 it is evident that two strains of White Marrow 

 are involved, the one in 309a being like Davis Wax in bearing the 

 coupled YZ, and the other strain only one of these factors, thus permitting 

 the appearance of self-colored beans. In crosses 331 and 332 there are 

 certain irregularities due to Creaseback that will be discussed later. 



Most of our crosses among self-colored beans have yielded only self- 

 colored progeny, no mottled or white beans appearing. A list of such 

 crosses follows : — 



