Measurements of the Velocity of Translocation

Abstract

The progress of radioactive sucrose translocated in willow bark was followed by assay of frequent samples of sieve-tube eiudate from a severed aphid stylet. The time profile of the advancing radioactive sucrose was the same shape as, and coincident with, the distance profile of radioactivity extracted from a series of sections of the bark. From the slopes of comparable parts of the two curves estimates of the velocity of movement of the distance profile through the bark were obtained and these were checked by independent measurements of a different kind. All velocities measured were about 2 cm.hr.^-1 Sugar from more than one sieve-tube must be flowing out of the stylet. The logarithmic relation between radioactivity and distance is shown to be only an approximation to a much more complicated relation.