insoluble fission products that are absorbed by the plants in minimal amounts under normal conditions. The remaining portion of the radioactivity 1s found in the more soluble calciunstrontium fraction which is known to be actively absorbed by living plants. The marked difference between the percent of calcium-strontium fraction found in the plants from Engebi and that found in the soils indicates that the plants absorbed more of this fraction than any of the other radioactive materials present in the soil. Conclusions. Analysis of the data obtained from counts made of 57 samples of land plants collected after Mike detonation shows a correlation between distance of collection area from ground zero and amount of radioactivity in the samples. On the basis of these data no clear cut differences can he pointed out as to the relative activity between species or between organs of a plant. The problems presented by surface con- tamination make further interpretations unreliable. 4.7 Rate and Birds Collecting Methods. Attempts were made to collect rodents and birds at éach of the principal collecting stations although they were not always successful. Collections of rats (Rattus exulans) were made by setting live traps in the runways near the openings of the rat burrows. The traps were left overnight since these rats are, for the most part, nocturnal in their feeding habits. - 61-. Openings to the wa RSa ‘Tf