Metallic lotis, Auxin Action, and Chelating Agents 365 



5 hrs. of red light administered from the third hour after soaking. 

 The first internodes (mesocotyls) from simihir plants grown in com- 

 plete darkness were sectioned in weak green light (15, 18), 4 mm. 

 sections cut 2 mm. below the coleoptilar node being used. Both types 

 of sections were allowed to grow in the solutions in complete dark- 

 ness. All section elongation was measured after 24 hrs. at 25° C. 

 unless otherwise indicated. Potato discs used had a 9 mm. diameter 

 and were 1 mm. thick. They were cut from 'Katahdin' tubers of 

 selected large size and washed 24 hrs. in water before use (9). The 

 growth media contained 2 per cent sucrose, unless its absence is 

 specified, together with either 5 X lO'^M KCl, CaCla at 5 X 10'^^^ 

 or lower, or both KCl and CaCL, or more generally potassium phos- 

 phate buffer, 0.0 IM, pH 5.5. 



The Action of Some Metallic Ions on Growth 



In the first place the powerful growth inhibiting action of calcium 

 must be emphasized. Since this inhibition was first reported on 

 coleoptile sections in 1938 (23) it has been confirmed by many work- 

 ers; it was shown very strikingly in pea stem sections, which show no 

 similar inhibition by magnesium (24). Unlike other ions, calcium 

 does not promote growth at low concentrations (24). On roots the 

 effect is one of growth promotion, as has long been known, and in 

 recent years studied especially by Burstrom. 



Other ions, however, notably potassium (23), manganese (2), fer- 

 rous iron (19), and cobalt (12), promote growth. Some of the effects 

 of buffers are largely due to their potassium content rather than to 

 their anions — a fact often lost sight of. The action of Fe+2 has been 

 ascribed to two different effects (19) (see Discussion). Cobalt is particu- 

 larly powerful, being nearly 100 times as effective as manganese on 

 coleoptile sections. It also strongly promotes growth of pea stem 

 sections which show very little response to manganese (21). 



Two observations suggest that cobalt operates by way of the organic 

 acid metabolism: (a) when acetate is added growth is no longer pro- 

 moted, but is strongly inhibited; (b) in presence of cobalt the normal 

 excretion of hydrogen ions is prevented (21). On the other hand, 

 Busse (4), from the facts that cobalt causes the growth of coleoptile 

 sections to continue for a longer time than normal and that their 

 respiration is not promoted but slightly inhibited, has concluded 

 that cobalt inhibits a process of cell-wall deposition which otherwise 

 would have made growth slow down. 



Recently Dr. Kenneth Wright in my laboratory has extended 

 the cobalt effect to potato tuber slices (Figure 1). Preliminary experi- 

 ments with this tissue showed that the optimum concentration, about 



