[en] Application of diethyl sulphate onto G₁ cells of barley seeds resulted preferentially in chromatid-type aberrations in the root tips (193 chromatid vs 4 chromosome types). Artificially prolonging the G₁ phase by a 1-4 week storage of the treated seeds at 20% seed-water content led both to a manifold increase in the frequency of aberrant metaphases in the first mitosis and to a clear-cut change in the ratio of induced aberrations (7 chromatid versus 4052 chromosome types). Exposure of barley seeds to X-rays resulted in chromosome-type aberrations, and neither the number nor the spectrum of aberrations was changed by prolonging the G₁ phase