Relative Infrequency of Soybean Varieties Having Only One Factor for Yellow Cotyledon.

In the soybean there are two cotyledon colors, yellow and green. Both types are green in immature soybeans, but as the beans ripen, the green pigment fades out in yellow-cotyledon varieties, and persists in green-cotyledon varieties. In inheritance, yellow differs from green in possessing a factor or factors that cause the green pigment to fade out as the beans mature. In crosses between yellow and green cotyledon types, yellow proves to be dominant, and in Fz, a ratio of 3 yellow to 1 green, or 15 yellow to 1 green, is obtained according as one or two (duplicate) factors, DI and Dz, are involved. In a former paper (WOODWORTH 1921) it was stated that while all the data available indicated that yellow color of the cotyledons was dominant to green, yellow cotyledon varieties differed among themselves with regard to the factors D1 and Dz that cause the green pigment to disaQpear a t maturity. “Some, perhaps most varieties, as, for example, Auburn, possess only one factor of this nature, while others typified by Variety 8, possess two such factors.” It now appears that the reverse of this statement is true, that is, that most yellow-cotyledon varieties possess two factors instead of only one. This is borne out by a study of the results secured to date from crosses showing segregation in cotyledon color {table 1). Of the 27 varieties listed in table 1, 23, or eighty-five percent, possess two factors for yellow cotyledon. In contrast with this condition in soybeans, SHULL (1918) finds that types of shepherd’s purse having duplication of a leaf-lobe factor are less frequent than those having only one such factor. From this fact he argues that “the duplication of this factor has taken place at a relatively recent date.” Taking the same line of reasoning we may say that duplication of cotyledon factors in the soybean probably occurred at a remote date. The wild soybean, which is supposed to be the ancestor of our common