404 



W. P. Jacobs 



was found in the pith alone, but as much transport as in the com- 

 plete controls was found once the vascular area was included in the 

 transport section (13). The most obvious conclusion is that the 

 normal, high-speed transport of auxin goes on in the vascular 

 tissues of stems. 



Added auxin moves only basipetally in sections from the Avena 

 coleoptile so long as surface leakage is forestalled and so long as more 

 or less physiological concentrations of lAA (indole-3-acetic acid) are 

 added — this was shown by Went and White in 1939 (25) and con- 

 firmed by Soding and Raadts in 1952 (19). If one doubted the uni- 

 versality of strictly basipetal auxin movement, where should one look 

 for acropetal transport? Certainly not in seedlings, and probably 

 not in determinate organs. A portion of stem from an adult plant, 

 histologically much more complex than the coleoptile and so located 

 that one would expect upward movement of metabolites, would be 

 a likely guess. Internode 2 of adult Coleus satisfies these requirements 

 (11). In addition, Coleus is from a large family (Labiatae) hitherto 

 never critically examined in its auxin relations. 



When the auxin relations of a rigorously standardized clone of 

 Coleus blumei Benth. were investigated, substantial acropetal trans- 

 port of added auxin was found in internode 2 in addition to the 

 expected basipetal movement (Figure 6). Exhaustive refinements 

 of technique to prevent surface leakage — including lowered humidity 



No. 



Apex — ^ Base 



AA 



Curvature 



Relation of blocks 

 to sections 



Base 



Apex 



Curvature 



lAA 



No. 



10 



157 



8 



7.5 i 1.2 



0.9to.4 



5.5 I 1.0 



0.6 I 0.3 



49 



10 



8 



149 



16.6 



Auxin transported 



4.9 



44 



Fig. 6. Determination of acropetal and basipetal movement of auxin in sections 

 cut from young inlernodes of Coleus wlien 2 mg/1 of indole-3-acetic acid in agar 

 is added (shaded blocks). The apical end of the section is designated A, lAA 

 represents the collected auxin calculated as though it were all indole-3-acetic 

 acid. From Jacobs (11). 



