398 W. P. Jacobs 



status of our knowledge of auxin movement in shoots of higher plants.^ 

 Our emphasis will be on evidence concerning auxin movement as it 

 relates to the yiormal physiology of the plant. \\^& will eschew 

 pharmacological studies, the movement of substances not known to 

 occur as native auxins, and papers which infer auxin movement from 

 some other effect presumed to be controlled by auxin. 



The literature can be divided quite sharply as follows: (1) papers 

 published before 1940, which present the general view that the 

 normal movement of auxin is strictly basipetal and is remarkably 

 uninfluenced by any sort of external factor; (2) more recent papers, 

 in which auxin movement has been found to vary with temperature, 

 ontogeny, type of tissue, and physiological condition, and in w^hich 

 even substantial acropetal movement of physiological significance 

 has been found. 



The first 10 years of research on auxin movement gave results 

 which are well summarized in Went and Thimann's monograph (24). 

 The general view was that auxin moved oyily from the apex toward 

 the base — there was no acropetal movement even when an external 

 supply of auxin was added to the basal end of the isolated section. 

 The amount of auxin moved basipetally was reported to be un- 

 affected by gravity, light, or an externally applied electrical gradient. 

 The calculated rate of movement was 7 to 15 mm/hr and was con- 

 sidered not to be affected by temperature (20). Also, as one added 

 more and more auxin to the top of the sections, more and more 

 auxin was transported — that is, there apparently was no saturation 

 of the transport-system (20, 23). Since a phototropic curve in the 

 intact seedling moved strictly apex-toward-base, too, and at a rate 

 corresponding to that reported by van der Weij for auxin, the results 

 with isolated sections were taken as applying to the intact plant. 



Before we turn to more recent work, there are a few points ^ve 

 should emphasize. First, note that most of the detailed papers on 

 auxin movement dealt only with the organs of seedlings — particularly 

 with coleoptiles of Avena and hypocotyls of legumes. Second, the 

 papers of van der Weij (20, 21) are the main source of information 

 on rate of movement, amount transported relative to amount added, 

 temperature independence, etc. This is unfortunate: anyone w^ho 

 critically reads van der Weij's 1932 paper is bound to be awed at 

 the number of exact, quantitative conclusions derived by careless 

 procedures from the inexact data. For instance, in 12 of the 14 

 experiments in which acropetal movement was looked for, auxin was 



^ Auxin movement in roots is not covered for a variety of reasons, among 

 tlicm being the paucity of critical work, the probably more complex auxin 

 metabolism in roots, and in particular the reviewer's lack of first hand experience 

 with auxin relations in roots. 



