S U M M A R YSpores were liberated at 0.25 and 1.0 m. above grass. Airborne concentrations at twenty or more points in the spore cloud were measured with specially designed and calibrated miniature suction traps, operated off a portable vacuum system. Deposition in the downwind direction was measured on artificial surfaces on the ground. Measurements were made up to 10 m. from the source.The observed increase in horizontal cross-wind standard deviation of the Lycopodium cloud agreed well with 0. G. Sutton's theory, but was incompatible with that of W. Schmidt.The coefficient of deposition, p , calculated from mean cloud concentration per C.C. and deposition to ground per cm.2, as well as the velocity of deposition, v g , varied with distance from source. Both p and vg were larger for Lycopodium than for Ganoderma, and at the greater distances tested, vg approximated to the expected terminal velocities of the particles in still air.The total number (Q") of Lycopodium spores liberated in each experiment was known, and tentative estimates of the proportion deposited within the sampling area indicated that, under day-time winter conditions in England, the cloud lost not less than 1 3 to 24% of its load within 10 m. of the source.

No abstract

No abstract

No abstract

In twelve experiments known quantities of Lycopodium spores (in five with spores of Podaxis) were liberated into the open air artificially from a point source, under different meteorological conditions, and trapped on 'Vaseline '-coated slides, placed horizontally at: 2-5, 5.0, 10.0, 15.0, 20.0, 25.0 and 30.0 m. from the source, along from five to thirteen radii (20' apart in some experiments, and 5" or 1 0 ' apart in others).The size of spore had little effect on the relative numbers of Lycopodium and Podaxis spores deposited at different distances (the deposition gradient), but from a cloud containing ten times as many Podaxis as Lycopodium spores over twice as many Lycopodium were deposited per unit area as were Podaxis spores. The rate of deposition is thus approximately proportional to the volume of the individual spore.Estimated percentage recovery, within the sampling area, of Lycopodium spores liberated varied from 5'4% (afternoon in wind of 4'4 m./sec.) to 91.6% (night in wind of 0.8 m./sec.). Recovery of Podaxis varied from 0.3 % by day to 1.6% by night. The results of these experiments are examined in the light of the statistical theories of W. Schmidt and 0. G. Sutton, which formulate atmospheric diffusion by eddies, and are found to be in closer agreement with the latter. The values of the parameters 'm' in Sutton's equation agree excellently with his theoretical values, but the values of the parameter ' C' are more variable.

No abstract

No abstract

No abstract