1. The biochemical analyses on certain colour pigments of flowers, such as anthocyanins and aurone glycosides, have been carried out spectrophotometrically in the snapdragon, Antirrhinum majus. Varieties and strains used were consisted of a certain diploid and tetraploid forms having the corresponding genotypes of pigmentation, and the patterns of relative concentrations of anthocyanins and aurone glycosides were compared with those varieties and strains. 2. As the result of quantitative spectro-photometric analyses upon the a ntirrhinin concentration with some red-flowered tetraploid varieties, it was made clear that the decreasing of M gene accompanied by the increase of m gene. had effected a reduced synthesis of antirrhinin, and, in consequence, that from the comparison of diploid and tetraploid forms, the increasing amount of M genes had directly correlated with a reduced antirrhinin formation in the red flowered varieties and with a reduced pelargonin synthesis in the orange flowered varieties. 3. A homozygous tetraploid varieties in reference to M gene, the crimson-red flowered one, showed a definite factor-dosage effect in the degree of pigmentation as compared with its corresponding diploid form, having the homologous genotype to its tetraploid form. The former could synthesize the antirrhinin 25%-40% more in amount than that of the latter. 4. The aurone pigment (aureusidin glycoside) in petals, was observed to be synthesized twice as much in amount in the tetraploid forms as in the diploid ones, which have homologous genotypes to the former. A certain heterotic phenomenon on the synthesis of aurone pigment in palate petals should be noticed in some F_1 hybrid individuals.