Somatic and genetic effects of incorporated strontium-90 and cesium-137 in the small cruciferArabidopsis thaliana, race Estland, were studied. The uptake and distribution of the radionuclides in the treated plants (M1) and their progeny (M2) were determined and the approximate radiation dose received was calculated.A significant increase in plant height and acceleration of floral initiation in the M1plants was observed. This was most likely a radiation effect rather than an ionic (or chemical) effect. The early flowering was consistently observed in several subsequent tests with acute gamma-ray seed treatment at 0.3 krads or 3 krads. The early floral initiation was not maintained in the M2progeny despite measurable quantities of radionuclides transferred through the M1seed to M2progeny, exposing the latter to low level chronic beta-ray exposure.The M2from90Sr- and137Cs-treated plants exhibited gross physiological changes (loss of apical dominance, dwarfism, gigantism, fasciation, etc.) and heritable mutations which persisted in the M3.