The absorption of I3'Cs by the Lemma minor was measured in relation to the concentration of the radioisotope in water; the temperature, pH, and luminosity were kept under control. A method for the analysis of the results is illustrated. When applied to the present case, this method evidences the influence on the absorption of the potassiumcesium change, due to chemical affinity, of the natural growth of the organism's colony and of the light effect. The concentration factors have been determined for the above mentioned processes.

In Siena, over a period of 3 yr, atmospheric dust was collected by means of impaction and electrostatic precipitation. The radioactivity of the dust collected was analyzed and analysis was made of the particle size distribution. The relations of particle sizes and associated radioactivity are given and the effect of humidity is discussed.

Musca domestica was tagged at each stage of development-larva, pupa and imago-by means of three solutions of I3'Cs of different concentrations. Specific activity was studied throughout the organisms' life-cycle and into the ensuing generation. At each determination of specific activity, the concentration factor was studied in relation to the Contaminated matter. The biological half-life of lS7Cs is calculated. The degree of contamination transmitted to the exposed surfaces by the contaminated organisms was also studied.

Growths of Trifolium pratense were contaminated by means of three solutions of 137CsS04 having different concentrations. Each one of the three solutions was used for contamination at three distinct stages of the plant's development, in two different ways: contamination of the soil only and contamination by means of overhead irrigation.The specific radioactivity of the plants was followed from their contamination up to about 80 days after the first flowering. The concentration factor was calculated for each sample. Autoradiographs were also produced.