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B. O. Phinney 



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GIBBERELLIC ACID, ^G./PLANT 



Fig. 3. Dosage response curve for gibberellic acid, using the mutant, dwarf 1, for 

 bioassay. Measurements are for length of the first leaf sheath only. Each point 

 represents the mean of 10 measurements. When tlie log of lengths of both the 

 first and second sheaths is used, the dosage-response curve is linear over the range 

 of 0.001 to 10.0 Mg- per plant. Data from Neely (7). 



unknown(s) simultaneously as a single bioassay. Surfactant effects 

 have been found to be an important variable. Introduction of a wet- 

 ting agent or organic solvent into the solvent solution (water) will 

 increase the sensitivity of the bioassay fifty-fold (Figures 4 and 5). Be- 

 cause of this variable, all solutions to be assayed contain the wetting 

 agent, Tween-20, at the concentration level of 0.05 per cent by volume. 

 Organic solvents, as well as the wetting agent, Tween-20, have been 

 found to give no growth response by themselves. 



EXPERIMENTAL RESULTS 



Relative Activities of the Gibbercllins for Dwarf Mutants of 

 Zea mays 



The three gibbercllins GAj, GAo, and GA^ have been shown to 

 be active in promoting shoot growth for the mutants d^, d.-,, r/^, d-^, and 

 aui (9, 13). The relative activities of these three gibberellins and the 

 gibberellin, BF-II, have been determined for the GAg-responding mu- 

 tants (Table 1). Each gibberellin was applied to sets of ten mutant 

 seedlings at three dosage levels for the mutants d-^, do, d^, and dr, and 



