Deposition of AIr‐borne Lycopodium Spores on Cylinders

For the study of deposition of air‐borne particles on plant and trap surfaces a small wind tunnel has been constructed giving turbulent or streamline flow up to about 10 m./sec. The efficiency with which cylinders of from 0.018 to 2.0cm. diameter, coated with glycerine jelly, catch Lycopodium spores at wind speeds over the range 1–10 m./sec. has been measured experimentally with a Cascade Impactor, operated iso‐kinetically, as standard. Efficiency has been found to increase as wind speed increases, and as cylinder diameter decreases. Similar effects have been observed in the field. Efficiencies observed are lower than predicted by Sell and Glauert, but agree well with those predicted by Langmuir and Blodgett, except with the narrowest cylinders. The standard vertical sticky traps used in routine trappings of fungus spores, pollen, and crop‐protectant sprays and dusts have a low trapping efficiency.