Chemistry and Qrowth 



of causing initiation of adventitious root growth, inhibit 

 elongation of true roots, has been studied by Amlong (1936; 

 his paper has not been seen by the author) and by Macht 

 and Grumbein (1937). The latter workers studied a new 

 variable — the time of exposure of roots (of Lupinus albus ; white 

 lupin) to low concentrations of indole-acetic and indole- 

 butyric acids, and an unspecified naphthalene-acetic acid. 

 Concentrations as low as one part of acid in 5,000,000,000 

 of water or salt solution (/)H about 5) were tried. Instead of a 

 toxic effect, a small stimulation of root-growth was observed 

 24 hours after transferring the plants from growth-substance 

 solutions in which their roots had been dipped for 15-20 

 minutes ; an exposure twice as long usually produced a small 

 inhibition of root-growth. No estimate of error is given, 

 however, and it is not clear whether the plants not receiving 

 growth-substance were subjected to a control operation of 

 transference. 



Hare and Kersten (1937) have appealed to a final absence 

 of toxicity, towards plant roots, of dilute aqueous solutions of 

 indole-propionic acid irradiated with ultra-violet light, as 

 evidence of the disappearance of the substance. (They give 

 reasons for thinking that methyl anthranilate was formed). 



Unfortunately, none of the published values for minimal 

 doses of solutions affecting root-elongation is comparable with 

 the values for minimal doses able to produce cell-elongation 

 by the oat coleoptile test ; this is true even when oats were used 

 for determination of both types of activity. The minimum 

 dose producing bending of the coleoptile in the usual Avena 

 coleoptile test is determined from results of tests on single 

 plants, each plant being supplied with a minute dose of sub- 

 stance, of which it absorbs the whole or the greater part. On 

 the other hand, tests of the toxicity of growth-substances 

 towards roots have been made with batches of plants having 

 their roots bathed in relatively massive amounts of solution, 

 and the figures for the limiting doses that inhibit root- 

 elongation to a prescribed degree have not been furnished 

 as a dose absorbed per plant, as must be done for compara- 

 bility with the coleoptile test. In reported results of the oat 



79 



