1.A cytological investigation of the endosperms ofNigella damascenaandN. sativafixed at various intervals after pollination reveals that the nuclei in both taxa are uniform in size and shape.2.The haploid chromosome number in the two species is the same i.e.n= 6.3.Although the normal cytological constitution of the endosperm in either case is triploid (3n= 18), nuclei exhibiting aneuploid chromosome numbers do occur in small proportions.4.Cytological aberrations including dicentric bridges and tripolar anaphases are present.5.Polyploidy higher than 3nis not recorded. This absence of higher polyploidy may presumably be correlated with the uniformity noticed in the endosperm nuclei of both the entities.