SPRINGBOARD PLANT DISPERSAL MECHANISMS OPERATED BY RAIN

Abstract

The calyx tube and pedicel of Salvia lyrata serve as a springboard mechanism from which the nutlets are thrown out violently when raindrops land on the distal part of the upper lip of the calyx. The force of the striking raindrop depresses the springy pedicel and, when this returns to its normal position, the nutlets are thrown from the calyx tube as a swimmer is projected from a diving board. The nutlets become surrounded by a coat of extruded mucilage as soon as they are wetted. Ocimum basilicum and other members of the Labiatae have similar springboard dispersal mechanisms which are operated by raindrops. The plantlets or gemmae of the succulent plant Kalanchoë tubiflora develop on narrow outgrowths from the parent leaf. These attachments serve as springboards from which the plantlets are violently discharged by raindrops. The plantlets are cup-shaped and are very effective in catching raindrops. The splashing action of raindrops may sometimes be an important agency effecting the pollination of certain cup-shaped flowers such as those of Ranunculus. About eighteen rain-operated dispersal mechanisms are now recognized. These are distributed among four of the major groups of the plant kingdom and it is probable that some examples will be found in all phyla of land plants.