Auxin Polarity in the Coleus Plant

Transport of auxin in stems and roots of Coleus blumei Benth. was studied, using a new auxin assay technique, the pea-root test. This test is sensitive to auxin concentrations as low as 10-11 M and involves a positive stimulation of root growth by auxin. 2. Polar gradients exist in the Coleus plant, which run from a strict basipetal polarity in the vegetative stem apex to the opposite polarity in the root tip. 3. Flowering stems do not have a strict basipetal polarity but are capable of transporting auxin acropetally as well. 4. Evidence is presented suggesting that a diffusible substance or substances in the flowering apex can cause the incomplete polarity characteristic of flowering stems. 5. Phototropism experiments are reported which demonstrate that intact flowering stems transport the phototropic stimulus acropetally and that vegetative stems lack this capacity.