Studies On Plant Growth‐Regulating Substances

Eight series of aryloxyacetic, α‐aryloxy‐propionic, ‐butyric and ‐isobutyric acids have been synthesized, and their growth‐regulating activity has been assessed using six different test methods, viz. tomato‐leaf epinasty, Avena cylinder, Avena curvature, tomato parthenocarpy, tomato‐leaf rooting and the Went pea test. The ability to induce morphogenic effects in tomato plants was also studied. The results are critically discussed and shown to be consistent with the view that in tests involving only cell extension the presence of an α‐hydrogen atom is usually necessary for growth‐regulating activity to be shown. In tests in which cell division occurs this effect is not so clearly defined, though the presence of an α‐hydrogen does, in general, correlate with growth‐regulating activity.