Physiological Approach to Selective Action of 2,4-D 



241 



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Fig. 6. The influence of pretreatment (filled in circles) with phenoxyacetic 

 on the subsequent course of uptake of 2,4-D and the gain in fresh weight by 

 ments of (A) A. sativa coleoptile and (B) G. hirsutum stem. 



acid 



ing 300 mg/1 oi POA for 3 his. before they were transferred to a 

 solution containing 3 mg/1 of labeled 2,4-D plus the POA, while 

 others received no pretreatment but were put directly into 3 mg/1 

 of 2,4-D. 



From Figure 6 there is no doubt that there is a major specific dif- 

 ference in the influence of POA on the absorption of 2,4-D. For Avena 

 the reduction attains 72 per cent at the end of 24 hrs. In contrast, the 

 pattern of uptake by Gossypium is not materially altered by POA, 

 save that the time when the rate becomes negative is shifted from 6 to 

 12 hrs. 



Table 1. The uptake of 2,4-dichlorophenoxyacetic acid 

 by segments of Avena coleoptile and Gossypium stem in the pres- 

 ence and absence of phenoxyacetic acid (POA). 



Sign, diflr. (P = 0.05) 



