PHYSIOLOGICAL STUDIES ON SAP FLOW IN THE SUGAR MAPLE, ACER SACCHARUM MARSH.
Sap flow from the stumps of sugar maples was over five times as great as that from the trunks of the same trees, which were detached in November, January and March. There was no consistent variation in the sugar concentration of sap samples drawn from stumps and trunks, but samples taken from points above girdles were consistently higher in sugar than those taken from below.Sap flow is attributed mainly to the activities of living cells, and it is suggested that the oxygen concentration of the sap and the release of hydrostatic pressure in tapped trees are related to cell activities.The beneficial effect of alternating cold nights and warm days on sap flow is attributed to an increase in availability of oxygen to the living cell through the agency of the relative solubility levels of oxygen in water at low and high temperatures.