Dynamic Functionality of Drip Tips on Tropical Leaves*

Tropical vegetation in areas with high humidity are characterized by leaves having elongated tips. When it rains, water droplets accumulate at and fall from the elongated leaf apex, giving rise to their name: drip tips. Whether drip tips enhance the efficiency of water shedding from leaves, however, is poorly known. The goal of this study is to investigate whether drip tips lead to greater water shedding from leaves in high humidity environments. We constructed model leaves with four different tip lengths and one without any tip length. Two high-speed cameras were used to capture simulated water drops on the model leaf surface to measure the vibrational frequency and amplitude when the water sheds from the drip tip. The volume and mass of the water droplets are recorded with the addition of a force sensor measurement and the deflection of the model leaf. The frequency, mass of the water, and deflection of the model leaf are analyzed with a simple cantilever beam model to investigate the biomechanics of the drip tip. In the absence of a drip tip, our model leaf commonly exhibits a freely singular droplet (dripping) characteristic. On the other hand, we observe a rapid water jet-like behavior in leaves with longer drip tip lengths. The dynamics, mechanical properties, and leaf tip length of the leaf model are compared to tropical plants that have drip tips in the forest understory of Brunei, on the island of Borneo.