WILLIAM P. JACOBS 



Princeton University 



The Polar Movement of Auxin in the Shoots 



of Higher Plants: Its Occurrence and 



Physiological Significance 



The manifestations of polarity during development and regeneration 

 are among the most striking and widespread phenomena in biology. 

 In vascular plants, to cite a few examples, polarity is evident in the 

 regeneration of roots on stem cuttings, in the basipetal reactivation of 

 cambial cell divisions in the spring, in the basipetal movement of 

 the phototropic curve in grass seedlings, and in the basipetal regen- 

 eration reported for xylem cells. These and other polar phenomena 

 during development have been known since the turn of the century. 



Hence, it was with the greatest interest that the work of Frits 

 Went was received in 1928. In an extensive and elegant paper (22), 

 Went reported the first separation of a plant hormone (later called 

 auxin) outside the plant, described a quantitative bioassay for the 

 hormone, elucidated many aspects of the role of auxin in the photo- 

 tropic curvature of oat seedlings, and — of particular interest for 

 this paper — provided evidence that auxin could move only from 

 the apex toward the base in sections isolated from the seedling. 



The significance of the polarity of auxin movement in explaining 

 the various developmental manifestations of polarity was quickly 

 realized; and all the polar phenomena mentioned above — plus many 

 more — have in the intervening years been attributed to the action 

 of polarly-moving auxin. 



That a substance having such manifold effects should be the only 

 hormone known to us which has such strictly controlled polar move- 

 ment within plant tissue makes that polarity of great interest. Ac- 

 cordingly, this paper will attempt to review critically the present 



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