The water-transport capacity of leaf venation is positively related to the leaf-lamina area, because the number and diameter of vein-xylem conduits are properly controlled to match the lamina area. Taneda and Terashima investigate how these co-ordinated relationships are achieved by studying the midrib xylem of leaves of tobacco, Nicotiana tabacum, and find that the developmental rates of the lamina area and the midrib-xylem characteristics change in a co-ordinated manner. Exogenous application suggests that IAA derived from the leaf lamina plays a crucial role in the development of the leaf venation.
