AbstractDirected Transport and Hormones — Value of Isolated Leaf as Experimental Material.Local application of aqueous phytohormonal solution (0.1 ml of various concentrations, from 50 to 0.025 mg‐l−1, of IAA, 2,4‐D, NAA, BAP, GA3) on isolated leaves influences the direction of ion transport. All tested hormones are efficient but the action depends upon the ionic species [positive action with32P,35S,36Rb (K), but null with45Ca or46Cl]. The movement of ions occurs through the phloem tissue and is not a cell‐to‐cell transfer. Competition between different parts of the leaf is demonstrated (a) between petiole which appears to be an important attractive centre and other parts of the leaf; (b) in a depetioloted leaf, between different centres induced by different phytohormones. In this respect, GA3appears to be the most efficient hormone in the tested material — leaves ofPelargonium zonale(L.) Aiton.The effects on directional transport are discussed in relation to other processes controlled by hormones, for instance growth, senescence, protein synthesis. A direct relation of directional transport with growth or delay of senescence may be discarded. The value of isolated leaves as simplified experimental systems is underlined by the fact that weak hormonal doses are efficient (0.025 mg.l for GA3and 0.5 mg.1for 2,4‐D) as compared to the higher doses used in othe