The role of petioles in light acquisition by Hydrocotyle vulgaris L. in a vertical light gradient

In natural herbaceous vegetation plants are exposed to a vertical light gra dient. In experiments, however, morphogenetic responses of stoloniferous pl ants to shade have nearly always been tested under homogeneous shade condit ions. In this study we simulated a vertical light gradient and found that t he response of Hydrocotyle vulgaris in this gradient differed considerably from the responses to homogenous shade. Petioles grew longer while at the s ame time the specific weight of petioles increased. The elongated petioles raised leaf-blades into better-lit places resulting in higher biomass. Thou gh leaves in the light gradient started their growth under low-light condit ions, the size of the leaf-blade was the same as in high light. Internodes were longer than in homogeneous shade conditions but specific weight decrea sed, probably due to increased allocation to the fast-growing petioles.