Hydathode
A hydathode is a type of secretory tissue in leaves, usually of Angiosperms, that secretes water through pores in the epidermis or margin of leaves, typically at the tip of a marginal tooth or serration. They probably evolved from modified stomata. It is involved in guttation, where water is released from the top in order to transport the nutrients in the water from the roots to the leaves. Hydathodes are connected to the plant vascular system by a vascular bundle.
Since the liquid being extruded is from the xylem it also contains salts, sugars, and organic compounds dissolved in water and this is sometimes seen to crystallize on evaporation, forming a white powdery substance on the leafs edge. This crystallisation is very obvious in halophytes, plants adapted to live in high salt environments, and consequently the hydathodes are known as salt glands in those species.
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