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IntroductionSap flow in the maples occurs in great profusion under conditions and in a season during which few other species of plants exhibit this phenomenon. It is known to vary from year to year, from place to place, and from tree to tree, yet everywhere it follows the same general pattern. In many of its characteristics it does not seem to conform to the theories advanced to account for its occurrence. It cannot be ignored, yet it never has been satisfactorily explained.Over a period of many years, a number of theories have been advanced to account for the mechanism by means of which water is moved to the tops of plants. Most A review of literature on the subject indicates that more than one mechanism may be responsible for movement of water to the top of the plants. The "root pressure, " the "vital " or living cell, and the "cohesion of watery" theories have been ad-vanced as forces individually capable of doing the work. For an extended discussion of each of these see MEYER and ANDERSON (8). They state that most plant physiologists agree that the cohesion theory explains the principal mechanism involved in the transportation of water, while the root pressure and living cell theories are of minor importance. The investigations of CLARK (1, 2) in Massachusetts, JONES and his co-workers (3, 4, 5, 6) in Vermont, and MORSE and WOOD (9,10) in New Hampshire are more directly concerned with the characteristics of sap flow in maple

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