Translocation velocity and specific mass transfer in the sieve tubes of Fraxinus americana L.

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Abstract
The ratios of sugar concentrations (sucrose/stachyose, raffinose/stachyose and sucrose/raffinose) in the sieve-tube exudate of Fraxinus americana L. undergo slight diurnal fluctuations. These “ratio waves” have been found to move down along the stem of trees at a velocity of 30–70 cm/h. They are, in contrast to the “concentration waves” of Huber et al. (1937), independent of the absolute exudate concentration and thus unaffected by hydrodynamic pressures changes in the xylem. The velocity is of the order of magnitude required by the mass transfer equation and thus indicates that sieve tube exudate is a moving solution. Furthermore, the phenomenon enabled us for the first time to follow phloem transport over distances of 12 meters.