Exudation Mechanism of Tree Sap

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Sap exudation : The period of the starting point of the sap exudation of birch trees coinsides with that the earth temperatures become above 0℃. The amount of the sap exudated in the one season corelates with the atomospheric temperatures and the change in the amount of sap exudated within a day corelates with the changes in atomospheric temperatures. Production in the leaves in a summer influences the amount of sap exudation in the following spring.Water distribution : The sap in the tracheids disappears gradually towards winter and disappear completely in the period just before the sap exudation starts by the repetition of freezing of the xylem and its re-freezing. The recovery of the cavitation seems to be derived by the pressures in the roots. Actually, the swelling of the roots during the sap exudation process was observed. The process of the refilling of the sap in the tracheids of the xylem was photographically recorded by Cryo-SEM techniques. The osmotic pressures in the sap of xylem tracheids and the function of the water pumping proteins in roots and trunks are the next targets to be investigated.