Results from plant root uptake experiments, under glasshouse conditions, support this concept. Also, the annual precipitation is higher at the Roller Coaster sites than at other study sites. 5. The 239-240 Pu inventory estimates indicate that the standing vegetation contributes a rather insignificant portion of the total contaminant present in these aged fallout areas. Four plant uptake experiments have been conducted under glasshouse conditions to determine the significance of root uptake of 239-2405, and 241 Am by alfalfa, barley, soybeans, and wheat. Radiochemical analysis has been completed for the barley samples (the other plant samples await analysis). Results showed discrimination factors ranging from 1074 to 107? for 239-240), uptake through roots. Pu/Am ratios for soil and plant samples also showed greater root uptake of 241an 239-240 the ingrowth product, , relative to Pu from the aged source materials. EXISTING AND ANTICIPATED PROBLEMS It has been desirous during the past three years of sample collection to obtain information on the annual plant species. period, however, During this the environmental conditions have been unfavorable for the production of annual plants in the study areas. Again this year, poor production of winter annuals is probable (those which germinate in late fall and winter and are so spectacular when flower- ing during April and May). Because of the late spring rains, there may be adequate summer annuals, grasses, and forbs to collect some samples for radiochemical analysis. The supposition that the activity levels found on vegetation may be attributed largely to superficial contamination is based primarily upon two assumptions: (1) the residence particulate material is resuspendable and of small particle size (fallout particles entrapped upon plant foliage from aboveground nuclear testing generally ranged below 44-micron diameter), and (2) results from controlled plant 33