To date, there does not appear to be any data which clearly define the amount of Pu taken up by plants by their roots, largely because of the difficulties in delineating between that Some Pu on the surface and that within the leaves and stems. laboratory work by Romney et al. not yet published (1975) indicat- ed factors of 107? to 10°* between concentraions of Pu in soils compared to that within plants grown on soils taken from NTS to the laboratory where surface contamiation could be prevented with confidence. To what extent these factors represent the field cannot yet be evaluated, although general experience with such experiments indicates laboratory values are generally higher than field values. That leaf surface materials deposited from the environment may be absorbed within plant tissue has been recognized for some time. Cataldo et aZ. (1975) have provided some information on Pu translocation to other tissue subsequent to leaf contamination. In the absence of a solution vector, Pu was relatively immobile with respect to translocation to root and seed tissues. sequent to a simulated rainfall of 0.4 cm in 7 mins, Sub- they found translocation dependent on period of the life cycle in beans for aged Pu oxide. 1.8 x 1074, The values ranged from less than 8.6 x 107° to There does not appear to be any way to evaluate these numbers in terms of the more heavily cutinized tissues of NTS, but it might be supposed that for desert vegetation, the values might be even lower. Even if these values are accepted and extrapolated to the precipitation values of 10 cm for NTS, and the ratios of soil Pu to plant Pu are considered, the final values would probably not be detectable. In any event, for NTS vegetation values presented by Romney et al. (1975) would include Pu within plants as well as on the surface of plants and these values ranged from a high of 1.2 nCi/g dry tissue down to 0.012 nCi/g dry tissue. These values thus represent the ranges in amounts that grazing animals would have entering their digestive systems from shrubs to which must be added amounts from direct ingestion of contaminated soils and from grasses also in the area. 172 Smith et al.