Darwin (1880) Liaht Coleoptile- tp and is transmitted to the Tip of coleoptile Opaque cap growth zone. (no curvature) no curvature) Boysen-Jensen (1913) stimulus passes through such as mica. Mica sheet Mica sheet Tip removed inserted inserted Gelatinn tip and coleoptile Paal(1919) Tip removed Tip replaced Growth curvature Went(1926) coleoptile-bending assay for quantitative auxin analysis. Coleoptile tips Each gelatin Coleoptile bends in on gelatin block placed on total darkness:angle 20 20 15 10 多 10 46810 0.050.100.150200.250.30 b6efaeoptie IAA in gelatin block (mg/L)