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I I I 1 1 I I I I I I I I I .1 I I I .1 - III - primitive shapes to well-defined, ribbed extensions. Occasionally, sector-like extensions varied on the same crystal and showed various stages of development. Plates on which sector-like extensions emanated varied considerably. Some plates were plain while others were quite unusual, with double and even triple hexagonal plates, and sectoring of the plate. Plates on which sector-like extensions emanated were usually symmetrical with all six sides of equal length. Both air and ground observations indicate that these crystals can undergo breakup in the air and the sector-like extensions generally become separated from the plate. However, surprisingly, these crystals were often captured with the extensions intact. 4.2.9 Plates with Dendritic Extensions (P2g) The aircraft observations confirmed the findings of Hagono and Lee (1966) that plates with dendritic extensions grow at temperatures between -12 and -170C. In the air these crystals were observed as individual crystals and as parts of aggregates but they were not common either in the air or at ground level. Hexagonal plates from which dendritic extensions originate are at least 300 ~m in diameter. This result agrees with the findings of Ono (1970). The plates were usually plain and regular in shape with all six sides of equal length. Air observations indicated that the size range of these crystals was large with the crystal length generally between lSOO to 4500~m. Both air and ground observations showed that the crystals break up readily in the air particularly at the point of the extension to the plate, or within the delicate dendritic extensions.