Wittwer, S. H., and M. J. Bukovac. (Michigan State U., E. Lansing.)Quantitative and qualitative differences in plant response to the gibberellins.Amer. Jour. Bot. 49(5): 524–529. Illus. 1962.—The comparative biological activities of gibberellins A1through A9were evaluated, over a wide concentration range and in several test systems. All gibberellins were effective in promoting stem elongation of dwarf peas (Pisum sativum), and, with the exception of A8, epicotyl growth inPhaseolus vulgaris.Elongation ofCucumis sativusseedlings was strikingly greater with A4, A7, and A9than with the other gibberellins. With mutant dwarfs ofZea mays, A5and A9were the most active gibberellins ford3andd5, and relatively ineffective compared to A3ond1. Gibberellins A2, A7, and A8were less effective than A3on all dwarfs. Qualitative and quantitative differences among the gibberellins were noted on seedstalk elongation and flowering ofLactuca sativa, with A3the most active followed by A1, A7, A4, and A9. No flowering or seedstalk elongation occurred with A2, A6or A8. Parthenocarpic fruit growth inLycopersicon esculentumwas a function of dosage with all gibberellins. At the lowest levels, A5and A7were the most active, while at the highest levels all gibberellins with the exception of A8were equally effective. The results suggest a high degree of species and response specificity among the known fungal and higher plant gibberellins, and demonstrate the importance of utilizing a wide spectrum of plant responses and dosage levels in the biological assay of plant extracts for native gibberellins.