Table 1 . Growth effects of various phcnoxy compounds * {continued) . 



* Stimulating (Cs) and inhibiting (C/) concentrations (moles per liter) mdicated as their negative 

 logarithms (pCs = - log Cs). Effects not reaching the levels shown in the head of the table and 

 some other information are given in the following way. Oat coleoptile cylinder test: I indicates that a 

 significant inhibition occurs but does not reach 20 per cent. pC/-values have only been given in cases 

 in which no stimulation at low concentrations precedes the inhibition. Even typical auxins natur- 

 ally cause a final inhibition at high concentrations. r t a a 



t At a pC/-value denotes that the inhibition is weakened or eliminated by the presence ot iAA. 

 but this has been tested only for a limited number of substances. S indicates that a significant stiniu- 

 lation occurs but does not reach 40 per cent. R indicates that some reversal of the initial inhibition 

 occurs at higher concentrations, but that the growth rate does not reach the control level, n heat root 

 test: S indicates that a significant stimulation occurs but does not reach 20 per cent. AH substances 

 certainly give 50 per cent inhibition when applied in sufficiently high concentration. In the case ot 

 the antiauxins, this inhibition is presumably due to nonspecific toxicity, and pC,-values below 4.5 

 have usually not been determined. Flax root test: f following a pC/-value denotes that the inhibi- 

 tion is preceded by a significant stimulation at low concentrations. When the pC/-yalues tall be- 

 low 4.5 they have sometimes not been determined. The column "Effect of 1-NMSP indicates the 

 strength of the restorative effect of the antiauxin 1-NMSP on the growth of flax roots inhibited by 

 the substance at issue, and the column "Effect on 2,4-D" the strength of the restorative effect of 

 the substance at issue upon flax roots inhibited by 2,4-D. Type oj activity: The method of charac- 

 terization is schematical and semiquantitative. In cases where different tests indicate ditterent 

 types or degrees of activity, the formulation is the result of a compromise. 



t The stimulation of wheat root growth is preceded by a strong inhibition at low concentrations 

 (see Figure 4), which is possibly indicative of some type of auxin synergism. 



§ The restorative effect is preceded by a synergistic one at lower concentrations. 



II Action curve of unusual form, possibly indicating a synergistic component of the activity. 



[221 ] 



