Inheritance of Seed Color in Lactuca Sativa^

The mature fruit of lettuce is an achene or naked seed, the color of which is determined by the color of its pericarp. The pigments that give the seed its particular color seem to be localized in the pericarp tissues.^ The mode of inheritance of seed color is of immediate practical importance to those breeding lettuce for disease resistance, climatic adaptation, and desirable commercial characteristics. Unlike flowers of most other food crops, those of lettuce can be emasculated only with extreme diíBculty, if at all. In making crosses the breeder must remove the maternal parent's own pollen from the stigmas after the anthers have dehisced, but before the pollen tubes have entered the stigmatic tissues. As it is generally almost impossible to remove every grain of the maternal parent's pollen, both selfed and hybrid seed develop in heads in which pollen removal is attempted. Therefore, the breeder must know the mode of inheritance of some easily recognizable character by which he can distinguish hybrid from selfed plants in the Fi generation. Seed color is a character that can be used to advantage for this purpose. The cultivated varieties of lettuce (Lactuca sativa L.) may be roughly divided into 3 groups on the basis of their achene color. Of the 114 varieties of lettuce listed by Tracy ^ in 1904, 81 were indicated to have white, 30 black, and 3 yellow seed. Since then the trend has been even more toward the white-seeded varieties, until now there are only a few important varieties of the black-seeded type and no important varieties in the yellow-seeded group. In the white-seeded group, the color is fairly constant except for discolorations caused by premature harvesting, dampness, and other environmental factors. In the black-seeded group the ach enes range in color from reddish brown through dark brown to black. These different shades-probably have a genetic basis; however, the differences are not great enough to permit accurate classification in view of the minor color variations caused by environmental factors. There are also some shade variations among varieties in the yellow group Some da-ta have been published by Durst* and Thompson^ on the inheritance of factors for black and white seeds, but no report that deals with the factors for yellow seed has been found. The data of Durst and Thompson agree that black behaves as a monogenic factor