Plant physiology
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Studies of stem water in red-osier dogwood (Cornus stolonifera Michx.) using nuclear magnetic resonance spectroscopy indicated that most freezing occurs at temperatures above -30 C in cold-hardy and tender stems. Hardy and tender stems had about the same amount of unfrozen water at -40 C (0.28 gram of water per gram dry weight). ⋯ Fully hardy samples not slowly precooled to at least -15 C did not survive direct immersion in liquid N(2). The results support the hypothesis that cooling rate is an unimportant factor in tissue survival at and below temperatures where there is little freezable water.