Q.F. W. Went's classic experiment, in which the tip of an oat (Avena) coleoptile was excised and placed asymmetrically on agar blocks that were then applied to decapitated coleoptiles, first isolated and named the plant growth regulator now known as:

Auxin was discovered through a sequence of classic experiments: Charles and Francis Darwin observed that a canary-grass coleoptile bends toward unilateral light only if its tip is intact; Boysen-Jensen showed the tip's influence could cross a gelatin block but not an impermeable mica barrier, proving it was a diffusible chemical; and F. W. Went isolated the substance itself using excised oat coleoptile tips placed asymmetrically on agar blocks, whose diffused chemical alone reproduced the bending in a decapitated coleoptile even in complete darkness, and named it auxin. The principal natural auxin is indole-3-acetic acid (IAA), synthesised chiefly in the shoot apex and young leaves; synthetic auxins include NAA and 2,4-D. Its physiological effects include promoting cell elongation (the basis of the phototropic response with which its discovery story began), maintaining apical dominance (suppressing lateral …