Ahydathode is a type of pore, commonly found invascular plants,[1] that secretes water throughpores in theepidermis or leaf margin, typically at the tip of a marginal tooth or serration. Hydathodes occur in the leaves of submerged aquatic plants such asRanunculus fluitans[2] as well as herbaceous plants of drier habitats such asCampanula rotundifolia.[3] They are connected to the plant vascular system by a vascular bundle. Hydathodes are commonly seen inwater lettuce,water hyacinth,rose,balsam, and many other species.
Hydathodes are made of a group of living cells with numerous intercellular spaces filled with water, but few or nochloroplasts, and represent modified bundle-ends. These cells (calledepithem cells[4]) open out into one or more sub-epidermal chambers. These, in turn, communicate with the exterior through anopen water stoma oropen pore. The water stoma structurally resembles an ordinarystoma, but is usually larger and has lost the power of movement.
Hydathodes are involved in the process ofguttation, in which positivexylem pressure (due toroot pressure) causes liquid to exude from the pores.[5] Somehalophytes possessglandulartrichomes that actively secrete salt in order to reduce the concentration of cytotoxic inorganic ions in their cytoplasm; this may lead to the formation of a white powdery substance on the surface of the leaf.
Hydathodes are of two types:
