The plasticity of organ size and anatomy

Leaf size of many, if not most, annuals is correlated with the rate of development, or vigor, of individual plants and even of individual branches. Two related questions were considered: whether there are vigor-dependent anatomical differences between leaves of different sizes, and whether organ size could be a neglected plasticity, a response to the overall state of the plant rather than to specific environmental cues. Senecio vernalis plants were grown outdoors in pots of three sizes. When the first capitula appeared, groups of plants were transferred from small and medium pots to large pots. There were 7-fold surface area differences between comparable leaves of plants in small and in large pots. Leaves that had been fully formed when plants were transferred to large pots caught up;, reaching the leaf sizes characteristic of their new conditions. Stomata densities, vein length per unit area, and cross sections of palisade cells were measured. These parameters differed in large and small leaves, and t...