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- 122 - there were never more than a'few droplets on anyone plate. Riming was not observed on plates with diameters less than 300 ~m. This is in reasonable agreement with the findings of Ono (1969). Riming was not observed on star- like crystals. Riming was most common on warm region crystals. Thus needles, sheaths, and columns at temperatures above -lOoC were generally rimed. It appeared that riming of these crystals occurred from the surface to about 5,000 feet above ground level. Riming was not found on columnar crystals less than 50 ~m in diameter. This also agrees with the field results of Ortb (1969) and theoretical calculations of the collision efficiencies of droplets with cylinders, However, many columnar crystals with widths much greater than 90 ~:n ,,[ere observed without any riming. Ono states that nearly all columnar crysta).:J collected having widths greater than 90 ~m were rimed. In the present study, the riming was often light, with seldom more than ten frozen droplets ,on a single crystal. However, heavier riming was observed on occasions. Because of the light degree of riminR, the size and locations of the droplets on the crystals were clearly observable. Airborne observations indicated that the frozen droplets on the crystals ranged from about 25 \.1m to 150 ~m in diameter with an average diameter of about 50 \.1m. Ono found that frozen droplets on warm columnar crystals were 20 to 70 \.1m in diameter. However, the columns collected by Ono were much shorter in length, and therefore narrower, than the columns collected by us. It appeared that in most cases, the droplets were sufficiently heavy to change the fall orientation of both hexagonal plates and columnar crystals. Thus, the edge on which riming occurred subsequently became the leading edge 1 l l I- I I I- I I 1 1 I 1 1 1 I I I I