SEED COAT COLOR IN GARDEN BEANS. 65 



of the letters have been used to designate more than one color, or colors, 

 of different genetic origin, but always similar colors, and usually those 

 that on first encountering we could not certainly differentiate. For ex- 

 ample, the B seed colors of Blue Pod Butter and Bountiful are similar 

 in appearance, but of entirely different genetic constitution, and can be 

 with some difficulty distinguished from each other in the field. It has 

 been the aim to use a given letter within a given cross always for the same 

 color character, and it is thought that this has been usually successful. 



The appearance of pigment in the seed coat of beans is usually the ex- 

 pression of a complex factor or the concurrence of several factors. In the 

 absence of any one of the elements of this factor complex the beans are 

 unpigmented. If this be the case, crosses of non-pigmented beans may 

 give rise to pigmented offspring. One such cross has been encountered in 

 this work, that of Davis Wax X Michigan White Wax. This does not 

 signify that such crosses are rare, for only three have been made in the 

 course of this work, the other two, Creaseback X Burpee's Fordhook 

 Favorite, and White Marrow X Burpee White Wax, yielding only non- 

 pigmented offspring. As previously reported, numerous crosses of plants 

 bearing white flowers have given rise to plants with pigmented flowers, 

 but all these have been accompanied by pigmented seeds. Had the pos- 

 sible results from intercrossing non-pigmented beans been realized from 

 the first a much larger number of such crosses would have been attempted. 



Crosses of Pigmented with Non-pigmented Beans. 



We have a white-coated bean whenever one or more elements of the 

 factor complex for pigmentation are absent, and crosses of such plants 

 with pigmented plants have shown dominance of pigmentation. The pro- 

 portions of pigmented and non-pigmented beans in the F2 generation 

 have been approximately 3:1, yet most crosses show departures from this 

 ratio that, in view of the large numbers involved, may be significant. 

 These results are shown in Table I. In some crosses there is an excess of 

 pigmented beans and in others a deficiency. We have been unable to 

 settle upon any theory that will explain in detail these seeming irregu- 

 larities. If the non-pigmented parent lacks more than one element of 

 the pigment complex an excess of non-pigmented beans in F2 would 

 result, — an explanation of the observed excess of white beans that may 

 or may not be correct. It is possible that the excess of pigmented beans 

 might be explained on the basis of a complex pigmentation factor were it 

 thoroughly understood, but we are unable at present to offer adequate 

 explanation of all the departures from a 3:1 ratio that have been observed. 



Some of the crosses involving Creaseback show very great departures 

 from a 3:1 ratio. In 97a and 331a the number of white beans is very few. 

 Both these must be crosses, for Creaseback is a pole bean, and pole beans 

 have appeared in considerable numbers in 97a, and most of the beans in 

 331a were entirely unlike Warwick, the female parent. This behavior of 

 Creaseback will be more fully discussed later. 



