When conditions are such that the absorption of water greatly exceeds transpiration, the excess of water escapes in the form of liquid trough structures called hydathodes present at the vein ending margins of leaf. This type of exudation of water is called guttation. The phenomenon of guttation is not universal.
Guttation is mostly exhibited by herbaceous plants e.g., Balsam, colossi etc. growing in moist, warm soil and humid conditions of atmosphere. It mostly takes place at night or early in the morning, when there is no transpiration and root pressure is high. The fluid which oozes out in guttation contains a variety of dissolved inorganic and organic substances.
Guttation takes place through structures called hydathodes. The hydathodes remain open whole day and night and are connected with veins. Each hydathode opens to the exterior by a pore called stoma.
The stoma is surrounded by two guard cells and open. Hydathode entire leaf showing position, B-V.S. of leaf internally into an air chamber just ‘ through hydathode below the air chamber there is a group of parenchyma tons cells with intercellular spaces called epithem.
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It lays inside the leaf below the epidermics mostly towards the margin or tip of the leaf. The xylem vessels and tracheas open just behind the epithem. The exudation of water in the form of liquid drops takes place through stoma.