The duration of the mitotic cycle and its phases has been determined in the root tips of seedlings from brown and black caryopses ofHaynaldia villosa, by autoradiographic technique after labelling with m3H-thymidine. The total duration of the mitotic cycle was found to be 12h in brown caryopses and 9.5h in black caryopses. As to the time length of single phases, the greatest difference between the two kinds of caryopses was foun dat the level of G1phase. The possible significance of these differences is discussed.