The vulgare-spelta locus on chromosome 5A of two typical cultivars, Large White emmer and Vernal emmer, of Triticum dicoccum SCHUBL., a species of tetraploid wheat (2n=28. AABB) with keeled glumes and brittle rachis, was genetically studied by crossing them to aneuploid lines of T. aestivum (L.) THELL. ssp. vulgare MK (2n=42, AABBDD). It was found that they have the spelta gene, q Thus, for these two cultivars, a previous assumption, which had been made mainly on the basis of plant morphology, was verified. The differentiation of spike type was rationalized between these varieties and another variety, liguliforme, which had previously been found to carry the vulgare gene, Q. It turns out that the rachis brittleness, a key character to distinguish dicoccum from the rest of the cultivated tetraploids, may not be determined simply by the presence of the spelta gene, q. Besides spike type, glume-coloration pattern is found to be a major difference between the two groups.