374 K. V. Thiynann and N. Takahashi 



experiments, though extensive, have yielded no conclusive result. 

 It was at first found that while EDTA alone had no effect, yet in 

 the presence of both lAA and EDTA a significant amount of Ca^s 

 was lost from the sections and recovered in the growth solution. 

 Subsequent more extensive tests have revealed a degiee of variation 

 between experiments which makes this result doubtful. More exten- 

 sive washing of the sections has not greatly reduced the variation. 

 It must be concluded that if EDTA does remove any calcium it does 

 not do so when added alone, and even the combination of EDTA 

 with lAA removes so little, if any, that it is at the borderline of 

 significance even with the highly sensitive radioactivity method. 



The chemical and photometric calcium determinations of Ng 

 and Carr (14) lead to the same conclusion. 



DISCUSSION 



One possible explanation of the large growth promotion which 

 EDTA causes in presence of auxin might be merely that its action 

 is proportional to the amount of elongation occurring. This is nega- 

 ted not only in Figure 3, but also by the data of Table 2 (and of 

 numerous similar experiments) which establish that first internode 

 sections in low auxin concentrations elongate more than coleoptile 

 sections, yet show a smaller EDTA effect. 



The failure of EDTA to promote growth appreciably in presence 

 of NAA or 2,4-D suggests that EDTA in some way protects lAA 

 from destruction within the tissues. While this is not impossible it 

 is not wholly satisfying for the following reasons: (a) destruction of 

 lAA in coleoptile sections in vivo is not very great, as witness the 

 high recovery of C" from carboxyl-labeled lAA in transport experi- 

 ments; (b) Figure 3 shows that at the lowest lAA level, where pre- 

 sumably destruction has its largest effect, EDTA is inactive; (c) in 

 Pisum sections, where lAA destruction is known to occur actively, 

 the effect of EDTA is relatively small. On the other hand, the strong 

 promoting effect of manganese on the lAA oxidizing system would 

 certainly give a basis for inhibition by a chelating agent. 



It seems more probable, however, that it is some other reaction 

 of lAA, perhaps its conjugation, that is metal-promoted and there- 

 fore sensitive to EDTA. It would be of interest to investigate the 

 several side reactions which remove lAA in vivo. 



At this point we return to the actions of specific metal ions men- 

 tioned at the outset. 



Recently, Shibaoka and Yamaki (19) have found that ferrous ions 

 promote growtii of Ax'cua coleoptile sections in I.\A but not in XAA. 



