These compounds activate the most common inducible degron in eukaryotes. Charles Darwin and his son Frances inadvertently postulated the existence of these compounds after (20[1])an 1880 experiment where they put tin hats atop coleoptiles (“ko-lee-OP-tiles”). Because these acids are neutral outside the cell but an·ionic inside, they can only be transported by efflux pumps down the polar axis. These derivatives of tryptophan cause cell walls to (*) expand in dark or downward-facing tissues. Although they normally inhibit abscission, these compounds also block ethylene production, which is why they act as herbicides in Agent Orange. These compounds promote apical dominance in competition with cytokinins. For 10 points, name these hormones that regulate plant tropisms. ■END■