Metallic Ions, Auxin Action, and Chelating Agents 373 



Table 4. Effect of soaking Avena seeds in calcium chloride on subsequent sensi- 

 tivity of the coleoptile sections to EDTA. All figures are elongation in per cent of the 

 initial length. Mean of four separate experiments. 



Sections from the plants of calcium-soaked seeds were now tested 

 for their reaction to EDTA, in parallel and on the same day with 

 sections from control plants. The results of four such experiments 

 (all done in sucrose plus KCl plus lAA 0.1 mg/1) are averaged in 

 Table 4. Without auxin the increments are very small and show no 

 difference. In presence of lAA the increment due to EDTA in the 

 control sections averaged 36.2 per cent of the length. In sections 

 made from plants pretreated with Ca+2 the increment averaged 35.6 

 per cent of the length. The agreement is good and the conclusion 

 clear; the growth promotion caused by EDTA in the sections enriched 

 in Ca+2 is no greater than in the controls. 



In these experiments the growth inhibition is known to be due 

 to Ca^^ which has been proved to be taken up by the tissue, yet 

 EDTA does not overcome it in the least. The growth promoting 

 effect of EDTA cannot therefore be due to chelation with calcium. 



In two papers which appeared after this work was done, Ng and 

 Carr (14) have shown that EDTA does not remove as much calcium 

 from intact or homogenized coleoptiles, or from filter paper, as does 

 citrate-phosphate buffer, and although their data show very small 

 and unsatisfactory growth promotion by EDTA (of the order of 5 

 per cent greater than controls) their conclusion that EDTA could 

 hardly act by chelating wall-bound calcium agrees with the above. 



The complementary approach to the same problem would be 

 to measure the actual loss of calcium from the sections during growth. 

 For this purpose seeds were soaked in Ca^^ CU as before and sections 

 cut for growth experiments from the resulting coleoptiles. After 24 

 hours' elongation the radioactivity both of the solution and of the 

 dried and powdered sections was determined. Unfortunately these 



