Measurements of the Velocity of Translocation

The progress of radioactive sucrose translocated in willow barkwas followed by assay of frequent samples of sieve-tube eiudatefrom a severed aphid stylet. The time profile of the advancingradioactive sucrose was the same shape as, and coincident with,the distance profile of radioactivity extracted from a seriesof sections of the bark. From the slopes of comparable partsof the two curves estimates of the velocity of movement of thedistance profile through the bark were obtained and these werechecked by independent measurements of a different kind. Allvelocities measured were about 2 cm.hr.^-1 Sugar from more thanone sieve-tube must be flowing out of the stylet. The logarithmicrelation between radioactivity and distance is shown to be onlyan approximation to a much more complicated relation.