%0 Journal Article %1 Hammel_67 %A Hammel, H. T. %D 1967 %J Plant Physiology %K bibtex-import, citeulikeExport freezebolism, freezing, snowgumpapermaybe, unread %P 55--66 %T Freezing of xylem sap without cavitation %U http://www.plantphysiol.org/cgi/reprint/42/1/55 %V 42 %X .Simmluiary. Freezinig of steimi sectioIns aln(d enitire twigs of hemilock ( 7'suga c(Inl(1- densis) has beenl demonistrated to occuir withotut increasilng thc resistance to the movemenit of water throuigh the frozen part after rewarmiing. This was interpretcdl to mnean that freezinig did not prodluce cavitation in the xylem sap even thouigh A) the sap was unquestionably frozeni; B) it containe(ldissolved gases; anlI C) it was under tension before freezing and after. Freezing stem sectionis of some other evergreen gymnosperms during the summer again produced no evidence for cavitation of the xylem sap. On the other hand, freezing stem sections of some angiosperms invariably increased the resistance to sap flow leading to wilting and death in a few hours when the sap tension was at normal daytime valuies at the time of freezing. These results were interpreted to mean that the bordered pits on the tracheids of gymnosperms function to isolate the freezing sap in each tracheid so that the expansion of water uipon freezing not only eliminates any existing tension bult also develops positive pressulre in the sap. Dissolved gases frozenl olut of sollution may then be redissolved uinder this positive pressuire as melting occlurs. As the bulbbles are reduiced in size by this ice pressure (levelope(d in all isolate(d tracheid, fturther pressuire is applied by the suLrface tension of the water agailnst air. If the bubbles are redissolved or are re(duice(d to stufficient small size by the time the tension retturnis to the sap as the last ice crystals melt, then the inter-nial pressuire from suirface tenision in any existing small btubbles may exceeed the hy(lrostatic tension of the melte(d sap and the bulbbles cannlot expand an(d will continuiie to dissolve.

@article{Hammel_67, abstract = {{.Simmluiary. Freezinig of steimi sectioIns aln(d enitire twigs of hemilock ( 7'suga c(Inl(1- densis) has beenl demonistrated to occuir withotut increasilng thc resistance to the movemenit of water throuigh the frozen part after rewarmiing. This was interpretcdl to mnean that freezinig did not prodluce cavitation in the xylem sap even thouigh A) the sap was unquestionably frozeni; B) it containe(ldissolved gases; anlI C) it was under tension before freezing and after. Freezing stem sectionis of some other evergreen gymnosperms during the summer again produced no evidence for cavitation of the xylem sap. On the other hand, freezing stem sections of some angiosperms invariably increased the resistance to sap flow leading to wilting and death in a few hours when the sap tension was at normal daytime valuies at the time of freezing. These results were interpreted to mean that the bordered pits on the tracheids of gymnosperms function to isolate the freezing sap in each tracheid so that the expansion of water uipon freezing not only eliminates any existing tension bult also develops positive pressulre in the sap. Dissolved gases frozenl olut of sollution may then be redissolved uinder this positive pressuire as melting occlurs. As the bulbbles are reduiced in size by this ice pressure (levelope(d in all isolate(d tracheid, fturther pressuire is applied by the suLrface tension of the water agailnst air. If the bubbles are redissolved or are re(duice(d to stufficient small size by the time the tension retturnis to the sap as the last ice crystals melt, then the inter-nial pressuire from suirface tenision in any existing small btubbles may exceeed the hy(lrostatic tension of the melte(d sap and the bulbbles cannlot expand an(d will continuiie to dissolve.}}, added-at = {2019-03-31T01:14:40.000+0100}, author = {Hammel, H. T.}, biburl = {https://www.bibsonomy.org/bibtex/297c95e908b529cb4420b0440fd2d75c8/dianella}, citeulike-article-id = {1523737}, citeulike-linkout-0 = {http://www.plantphysiol.org/cgi/reprint/42/1/55}, interhash = {1d9bb9bd4237dd37be44b2417f1eae1a}, intrahash = {97c95e908b529cb4420b0440fd2d75c8}, journal = {Plant Physiology}, keywords = {bibtex-import, citeulikeExport freezebolism, freezing, snowgumpapermaybe, unread}, pages = {55--66}, posted-at = {2007-07-31 06:20:30}, priority = {2}, timestamp = {2019-03-31T01:16:26.000+0100}, title = {{Freezing of xylem sap without cavitation}}, url = {http://www.plantphysiol.org/cgi/reprint/42/1/55}, volume = 42, year = 1967 }