An anomalous mode of segregation in respect to apiculus anthocyanin pigmentation observed in a fertile hybrid between a Japancse (Norin No. 1)and an Indian rice variety (Surjamkhi) was described. The apiculus color of Norin No. 1 is red and that of Surjamkhi is dark purple, whose genotypes havebeen determined as C^B Sp^a A and C^B SpA respectively after the gene symbols designated by NAGAO and TAKAIIASHI. C is a gene responsible for the production of chromogen and Sp, acting complementarily, turns it into anthocyanin. Both C and Sp form a mnultiple allelic scries, C^Bt>C^Br>C⁺ and Sp>Sp^dSp⁺. F₁ hybrid between them shows dark purple apiculus color. Its seedbearing fertility is nearly perfect (96%), though it shows a certain degree of pollen abortion (14%). In F₂ it segregated individuals with colorless apiculus which came up to about 30 per cent of the total, instead of showing the expected segregation ratio of 3 dark purple : I red, i.e., 3 Sp : 1Sp^d, accompanying remarkable decrease of individuals with red apiculus color (Table 2). A large part of the colorless plants showed tawny coloration in their apiculus at ripening, showing the effect of C^B observed when Sp or Sp^d is absent. The apiculus color at ripening of the remaining colorless plants was straw white, showing on effect of C^B. Segrefation of partial sterility also occurred in F₂ as shown in Table 3, in which one can detect no clear relation between the partial sterility and the types of apiculus coloration. The similar distribution of partial sterility in each of the classes is taken to show that the gametes of f₁ bearing noncoloredness were equally functional as those bearing coloredness in bringing forth the F₂ progeny. The mode of segregation of apiculus color observed in 83 F₃ strains originated from randomly taken F₂ plants, including 48 colored and 34. colorless ones, was various (Table 4 and 5 ). Some strains showed mono- and dihybrid segregation ratios, but others did rather complex ratios which could not tion between the partial sterility and the apiculus color was observed. Discussion was madd as to the mechanism which resulted in the segregation of individuals with colorless apiculus in F₂. Since the frequency of the appearance of colorless plants in F₂ was remarkably high, the mechanism due to autonomous mutations, C^B→C⁺, and Sp^d→Sp⁺, was concluded to be out of qucstion. It was suggested that the anomalous segregatisn might bc due to minor structural differences of chromosomes between the parental varieties which did not affect directly the parental varieties which did not affect directly the viability of gametes produced of F₁ hybrid. Though there were found some F₃ plants which seemed to be deficient in the gene loci in question by crossing them with tester varieties of known genotype, the authors could not attain to a definite conclusion as to the mechanism under issue.