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- 106 - 1 l I- 1 1 1 1 t I~ I- i 1 1 1 L 1 1 I~ I 1000 l-lm. Aircraft observations indicated the average diameter was about 350 llm. At ground level, plates as large as 3000 llm in diameter, with the average sornewherenear 700 llm, were observed. The discrepancy between air and ground observations appears to stem from the fact that larger plates could be collected more easily at the ground. Many larger hexagonal plates, with diameters well in excess of 300 llm, did not show any si.gn of dendritic growth at their corners. At the ~ound plain hexagonal plates up to 3000 l-lm in diameter were observed without any indication of growth at their corners.Ono (1969), on the other hand, observed dendritic growth on all plates larger than 300 l-lm in diameter. Some :texagona1 plates collected from the aircraft had "double growth." Frozen dro?lets could not be detected at the centers of these crystals, therefore, the double growth may have been due to the nature of the ice nuclei. Few hexagonal plates with double growth were observed at m:'ound level. However, this may be due to the sm~ller number of sin~le plates collected at the ground. Double growth on hexagonal plates was not common even higher in the atmosphere, and most of the plates observed on the gI'oundwere parts ofaggreStates. Air and ground observations indicated 'that thin hexagonal plates rarely broke up cue to collisions with other crystals and ag~regates. 4.2.5 Thick Plates (Clg and C1h) Our aircraft observations confirmed the results of Ono (1970) that thick plates grow between about -10 to -20oC. The thick plates were usually present as individual crystals. Thin hexagonal plates were much more common than thick plates. Gt-ound observations indicated that thick plates were not common, but those observed were individual crystals.