Winter Freezing in Relation to the Rise of Sap in Tall Trees.

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Abstract
Freezing of water under tension in a fine glass capillary resulted in bubble formation and breaking of the cohesion. Gas bubbles were formed also in tracheids of spruce wood when frozen and thawed. Supercooling in cut twigs of gymnosperms was produced experimentally, but not observed in situ. The unfrozen water in the xylem of Picea excelsa, Betula odorata and Acer platanoides, measured calorimetrically, amounted to a constant fraction (30-40%) of the dry weight, decreasing with temperature, but independent of the total water content, indicating that the unfrozen water was bound to the wood leaving sap within tracheids and vessels frozen.