The cell cycle of the root meristems of two species (to the left: Vicia faba, to the right: Tradescantia paludosa). Ochre: mitosis (duration: 2.0 or 3.0 h), blue: G1 (duration: 4.9 or 1.0 h), lilac: G2 (4.9 or 2.5 h): gap phases 1 and 2, red: S= synthesis phase (7.5 or 10 h). During S-phase, the DNA is replicated. A chromosomal equivalent consists of one chromatid during G1-phase and of two chromatids during G2-phase. The total duration of the cell cycle is accordingly 19.3 or 17.0 hours (according to U. GOODENOUGH: Genetics, 1978). 1978).