144 Fundamentals of Auxin Action 



Thus, it appears that translocation of auxins applied in large 

 amounts is accomplished by their being swept along by a carbohydrate 

 translocating system. Either light or the addition of sugars can bring 

 about translocation. Light without carbon dioxide is ineffective (Wein- 

 traub and Brown, 1950). Translocation is not carried out principally 

 in the xylem, for steam killing of petioles effectively prevents trans- 

 location {loc. cit.). 



Movement in Xylem 



Under certain circumstances auxins can be translocated in the 

 xylem. This can be deduced from the experiments of Hitchcock and 

 Zimmerman (1935) who showed that auxins applied to the soil can move 

 acropetally in plants, apparently in the transpiration stream. A 

 particularly graphic demonstration of transport in the xylem was 

 made by killing a section of stem with a flame, and showing that move- 

 ment of 2,4-D from the soil to the growing point was unimpeded 

 (Weaver and DeRose, 1946). No downward movement could be found 

 through the dead stem section. It seems unlikely that this type of 

 translocation occurs to any appreciable extent when auxins are ap- 

 plied as foliar sprays, but it does occur when the auxin is applied to 

 the soil or to a cut plant part, which gives direct access to the transpi- 

 ration stream. 



Movement in Oil 



The movement of auxins applied to plants apparently cannot be 

 explained entirely on the basis of the systems described so far, for a 

 puzzling report by Penfound and Minyard (1947) indicated that 

 treatment of leaves with an ester of 2,4-D applied in kerosene was just 

 as effective in weak light or dark as in strong light. The existence of 

 still another means of auxin movement was established by Rice and 

 Rohrbaugh (1953). They followed the movement of 2,4-D applied to 

 bean plants in kerosene, and discovered that in such an oil base the 

 auxin moved about the plant through the cell walls and intercellular 

 spaces by capillarity. This movement is independent of light and 

 sugars and has no polarity, of course. The form of the auxin had no 

 detectable influence on such movement; the acid, butyl ester and 

 propylene butyl ester of 2,4-D showed the same behavior. 



The rate of movement through the plant with kerosene was 

 studied by the use of radioactive 2,4-D. Carbon^^ was incorporated 

 into the carboxyl position of the auxin, which was applied in kerosene 



