The present study on inheritance of bulb color in onions continues work begun 10 years ago at the United States Department of Agriculture. Results obtained in F₁, F₂, F₃, and backcross progenies of several varieties and lines are explained by assuming that five major genes, I, C, G, L, and R (each with two alleles) interact, and segregate independently of each other. The five genes act in a specific order on a biochemical pathway that leads to pigment formation. A diagram for such a pathway, showing the action of each gene, is proposed. Four of the genes, I, C, L, and R, were reported previously by other workers. (L and R are the designations given by us to the complementary genes reported by (Jones and Peterson, 1952). The fifth gene, G, is proposed in the present study. The results of several of the crosses cannot be explained without its presence.

The density of golden yellow and red colors is apparently controlled by several microgenes; i.e., it is quantitatively inherited. Quantitative inheritance is not discussed in the analysis of the crosses, because this subject requires further investigation.

The study also further substantiates the presence of the four genes previously reported.