Metallic Ions, Auxin Action, and Chelating Agents 371 



surprisingly enough, it is not shown in combination with NAA or 

 with 2,4-D. Table 3 shows representative figures, the mean of three 

 complete experiments with each of these auxins. lAA at one or two 

 concentrations was included for comparison in each series; the con- 

 trast between the clear, positive effect of EDTA with lAA and its 

 slight negative effect with the other auxins is evident. 



Evidently, therefore, the action of the chelator is specifically con- 

 cerned with that of lAA. It is reasonable to suggest that its very 

 small but repeatable effect in the absence of added auxin is exerted 

 by potentiating the endogenous lAA. 



The Interaction Between EDTA and Calcium 



As stated at the outset the promotion of growth by chelators 

 might be due to their removing an endogenous growth-restraining 

 concentration of calcium. It follows that the chelator should also 

 be able to remove a growth restraint caused by externally added 

 calcium. In other words, growth inhibition caused by added calcium 

 should be antagonized by EDTA. Experiments to test this can be 

 carried out in two ways: the calcium can be added directly to the 

 growth solution or it can be taken up by the plants beforehand. The 

 former method has the obvious disadvantage that chelation of the 

 calcium can occur in the solution so that the effect on the plant is 

 masked. The second is in some respects more problematical but it 

 is freer from objection. While both methods have been used, and 

 lead to the same conclusion, only the second will therefore be 

 described here. 



Ave7ia seeds were soaked in CaCL solutions of various strengths 

 from 0.02M to 0.00 IM, and after 3 hrs. were laid out on filter paper 

 in the usual way. Sections were cut from the coleoptiles 72 hrs. later 

 and their growth compared with that of control sections (from seeds 

 that had been soaked in water), both being tested on the same day. 

 With low CaClo concentrations the differences were not always sta- 

 tistically signficant, but with 0.02M they were real. As a mean of 

 10 experiments in sucrose-KCl the control sections grew 38.9 ± 2.3 

 per cent, the sections from Ca-soaked seeds 30.5 ± 1-5 per cent. 



In order to be sure that this decrease in growth was due to calcium 

 taken up into the coleoptile, the procedure was repeated using Ca'*^. 

 After 76 hours' growth the plants were dissected and the radioactivity 

 counted. The activity expressed as percentage of the total was 

 distributed as follows (mean of 10 plants individually sectioned and 

 counted): roots 24, seed 39, coleoptile 32, leaf 5. Thus one-third of 

 the Ca^s taken up was present in the coleoptile. 



