Cytoplasmic nucleoids in the generative cell of mature pollens, sperm cells of pollens cultured in vitro and egg cell of mature embryo sac in Calystegia hederacea Wall, were studied by means of the DNA fluorochrome DAPI in conjunction with epifluorescence microscopy for in situ detection of cytoplasmic DNA in cells.

The specific combining ability differs greatly in the hybrid combinations of different type of cytoplasmic male sterility and among different traits of the hybrid combinations with the same type of cytoplasmic male sterility.