Polar Movement of Auxin in Shoots 399 



0* 1 9 



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LENGTH OF TRANSPORT, HOURS 



Fio-. 1. Determination of the rate of transport of indole-3-acetic acid (lAA) 

 through the intercalary meristem of the peanut gynophore as being 10 mm/hr. 

 Data on each of the 3 individual experiments are from Jacobs (10); but the heavy 

 line is the straight line which gives the best fit newly calculated by least squares. 

 The calculated intercept is at 0.30 hr. (as contrasted to the less accurate graphical 

 determination of 0.33 hr. in the original paper). 



found in the apical collecting block - yet van der Weij concluded 

 that auxin is not transported base toward apex. Again, to determine 

 each rate of movement, van der Weij needed to find the intercept 

 of a straight line (as in Figure 1): in 22 cases he used only 2 points 

 to determine the straight line. And in one of these cases, the line 

 actually drawn is at an 11° angle to the line determined by the two 

 points. These are serious matters, since the actual position of these 

 arbitrarily drawn lines determines his conclusions about both the 

 speed and intensity of auxin movement. 



The third point to emphasize is a source of error brought out 

 by Went and White (25). They reinvestigated auxin movement in 

 the Avena coleoptile, and found that when auxin was added to isolated 

 sections kept at the usual high humidity, auxin would move in the 

 film of water which formed on the surface of the sections. A sub- 

 stantial amount of van der Weij's difficulties was presumably due 

 to this artifact. Similarly, an unspecified amount of Went's (23) re- 

 sults were also attributed to surface leakage. - 



= The literature is critically discussed in terais of this and other sources of 

 error (12). 



