294 BULLETIN OF THE TORREY BOTANICAL CLUB [Vou. 91 from ground zeros and/or from midlines. Concurrently, the percentage of activity associated with particles < 44 (microns) and with particles < 88p in diameter show a marked increase. For a given detonation, the percentage of theoretical fallout activity* associated with particles of < 44, is inversely related to the amount of material incorporated in the fireball. Devices detonated as air drops at altitudes > 1500 feet have produced no detectable fallout within 200 miles of the Nevada Test Site. The local fallout from a balloon-supported device whose fireball did not intersect the ground, accounted for only 0.2% of the theoretical fallout activity produced by the detonation. For a similar balloon-supported device, whose fireball did intersect the ground, local fallout accounted for 2.12% of the theoretical total. Tower-supported detonations, with and without fireball-ground intersection, resulted in local fallout patterns containing 6.7% and 24.5% respectively of the total activity produced. Of all the radioactive material produced by nuelear detonations at the Nevada Test Site, < 25% of the total (and < 10% of the radiostrontium ) Table 6, Beta activity of fallout in relation to its particle size composition and distance from ground zero. Miles from G.Z. Particle Size < 44y 44-88 88-125 > 125 Total Fallout on Soil 12 2.3 1.9 1.8 94.0 4817 20 46 60 79 (% of activity in particle size range) 12.7 16.0 18.8 22.9 52.7 49.8 77.2 66.5 24.3 27.0 1.3 7.4 10.3 7.2 2.7 3.2 (Activity in ye/ft? at H +12 hrs) 2593 533 202 184 96 24.9 72.4 1.9 0.8 160 After: Baurmash et al. (1958). has been deposited as local fallout (Larson et al. 1960). Presumably, the remainder has been available for long distance transport and deposition chiefly in areas to the east and northeast of Nevada. 2. Tropospherie fallout. The fine radioactive debris released to the troposphere in southern Nevada maybe carried by high-altitude winds across the United States and around the globe in a girdle ranging from 30° to 60° north latitude. Some tropospheric debris has been observed to cireumnavigate the globe in a period of from 4 to 7 weeks (Glasstone 1957). Some tropospheric debris may be deposited by gravity fall, and some maybe deposited by impaction on vertical surfaces, but the removal of the major part Is probably accomplished by rainfall and other forms of moisture precipitation (Greenfield 1957). During the 1957 test series in Nevada, rainfall east of the Rocky Moun- tains contained considerable quantities of 1-12 day-old fission products. In * Based on an estimated gamma activity at H+1 hr of 3x10" euries per kiloton of yield.