A New Interpretation of the Mechanics of Pulvinar Movement

Abstract

KNOWLEDGE of the mechanics of pulvinar movement is based mainly on the work of Dutrochet¹, Pfeffer² and others conducted in the nineteenth century. They showed that if the upper half of the primary pulvinus was removed from the leaf of Mimosa pudica then leaf movement continued, although on a reduced scale. It was deduced from this that the lower half of the pulvinus is principally concerned with the movement, which was then accounted for in terms of loss of turgor followed by recovery. This early explanation of pulvinar mechanics is still widely accepted by workers in this field³, and has recently been used in drawing comparisons between the movement of guard cells and pulvini⁴. The results are briefly reported here of studies on leaf movement exhibited by Samanea saman Merrill and Mimosa pudica. In our view they cast doubt upon the validity of this explanation.