Polar Transport of Three Auxins 



413 



Fig. 2. 

 flower 

 time 1 



BLOCK 



The acropetal and basipetal transport of three auxins applied to sun- 

 stem sections in various concentrations. Symbols as in Figure 1. Transport 

 20 min. for lAA and NAA, 180 min. for IBA. 



tal directions was also measured. Each was presented in agar donor 

 blocks to sunflower stem sections. Concentrations of the auxins were 

 varied between 3 X lO-'^M and lO^Af. Assays of the receptor blocks 

 provide data such as those shown in Figure 2. Looking first at the 

 basipetal transport, it can be seen that each of these three auxins is 

 transported downward in the manner usual for lAA. The amount of 

 auxin transported is presented simply as the Avena curvature without 

 correction for difl;erences in activities in the Avena curvature test or 

 for length of transport period. It can be readily seen, however, that 

 downward transport was obtained, and that NAA and IBA were ap- 

 parently transported in somewhat smaller quantities than lAA. The 

 tests of upward transport show that within the range of concentra- 

 tions of donor blocks tested (10-^ to IQ-^AI) essentially no transport 

 was obtained. We can, therefore, conclude that each of these three 

 auxins is transported in a polar manner. 



A further comparison of the transport of the three auxins can be 

 made by measurements of the velocities of transport. Velocity of 

 transport was measured in the manner originally used by van der 

 Weij (9). Sunflower stem sections were provided with donor blocks 



