5. My working hypothesis on the yellow-orange endosperm is now as follows:

(a) Several Y-genes with complementary effects, similar to the A₁A₂A₃C R series for aleurone color. Of the Y-series, the known genes are Y₁ in chromosome 6, Y₃ in chromosome 2 and probably Y_x of Dr. Brunson, chromosome unknown. The y_x condition is lethal and the y₃ produces albescent seedlings (al gene).

(b) The Y₅ gene, isolated from Brazilian strains is complementary to Y₁ in producing yellow endosperm but is independent of Y₃ and so, also, of the other Y-genes of the series.

(c) The Y_D gene (D=determiner) producing the difference orange : yellow, found in Brazilian material and extremely influenced by modifiers. Similar gene found recently by Dr. Jenkins in chromosome 7.

(d) The Bn gene in chromosome 7, producing yellow pigment only in the aleurone layer. These "lemon yellow" seeds are detectable in stocks lacking one of the complementary Y-genes for endosperm color.