84 MASS. EXPERIMENT STATION BULLETIN 185. 



appear. These facts suggest that Blue Pod Butter lacks some factor 

 possessed by the other varieties, and, furthermore, that it is associated 

 •with a mottling factor. We have called this factor M. We have already 

 adopted the explanation of the phenomenon of mottling by assuming a 

 formula for Blue Pod Butter of PTYz, — that is, Blue Pod Butter lacks 

 one of the mottling factors, Z, while the other varieties shown in Table 

 XI. have this factor Z. Blue Pod Butter, then, lacks both Z and M, 

 while all the other varieties carry these factors. We can then express 

 the constitution of Blue Pod Butter by the formula PTYzmo, and Burpee 

 Stringless, for example, by PTyZMO, and the evidence is that Z and M 

 are always associated, or that we have another case of apparently perfect 

 gametic coupling. The varieties other than Blue Pod Butter must possess 

 additional determining factors for the various colors exhibited. These 

 will be dealt with later. 



It has been said that we have two series of pigments in beans, — one 

 bearing the red series, eAddently anthocyan, and the other what we have 

 called the yellow-black series. The crosses given in Table XL, excepting 

 343, 347 and 349, are of the latter nature, while these two crosses and 

 three in Table XII. are crosses with varieties exhibiting colors of the red 

 series. These behave like those given in the previous table so far as the 

 relation of their colors to the B of Blue Pod Butter is concerned. 



If we assume that it is the factor just discussed that is the determining 

 element for the class of pigment borne, and assume, further, that there 

 are two of these pigment modifiers, one of which, M, brings about the 

 formation of the yellow-black pigments, and the other, which we may call 

 M', the formation of those of the red or anthocyan series, we have a theory 

 that seems to explain the facts alreadj^ presented and others shown later 

 as well. 



The production of a totally pigmented bean, then, rests on the presence 

 of several factors. First, we must have P, in the absence of which we have 

 a white bean; second, T, in the absence of which the bean has an eye; 

 third, the presence of M or M', the former causing beans of the j'^ellow- 

 black series, and the latter, pigment of the red series. If neither or only 

 one of the mottling factors Y and Z are present the bean is self-colored, 

 while if both are present a mottled bean results. If P and T are present 

 and M and M' absent, the bean is buff-colored, shown in Blue Pod Butter 

 and the lighter shades in mottled beans. All colored varieties used in these 

 experiments carry Y or Z or both; and the factor M or M' or both are, 

 when present, always associated Tvith the factor Z. 



The Behavior of the Yellow-Black Determiners. 

 When the factors P, T and M are present, a buff or ecru colored bean 

 is produced. The presence of certain additional factors modifies this to 

 the various colors of the yellow-black series. These colors are black, 

 designated by G; coffee brown, designated by F; yellow, designated by 

 C; and a possible light brown or olive brown, designated by H. The first- 



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