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The below mentioned article provides a study note on the guttation in plant cells.
In some plants such as garden nasturtium, tomato, strawberry, Colocasia etc., watery drops ooze out from the uninjured margins of the leaves where a main vein ends. This is called as Guttation and takes place usually early in the morning when the rate of water absorption and the root pressure are higher while the transpiration is very low. The watery drops consist of water in which many inorganic and organic substances are dissolved. After the drops have dried the salts and organic substances etc., remain in the form of a residue on the margins of the leaves.
The phenomenon of guttation can be demonstrated by a simple experiment (Fig. 5.11 A). A well watered potted plant of garden nasturtium is kept under a bell-jar on a glass sheet. Before this, the pot is covered in a polythene bag to check the evaporation of water from the soil. The apparatus is made air-tight by applying vaseline. The bell-jar is connected to an aspirator. Air is sucked from the bell-jar by means of the aspirator. After a very short time watery drops will appear on the margins of the leaves.
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The phenomenon of guttation is associated with the presence of special types of stomata at the margins of the leaves which are called as water stomata or hydathodes. Each hydathode consists of a water pore which remains permanently open. Below this there is a small cavity followed by a loose tissue called as epithem.
The epithem is in close association with the ends of the vascular elements of veins (Fig 5.11 B). Under higher root pressure the water is given to the epithem by the xylem of the veins. From epithem the water is released into the cavity: When this cavity is completely filled with the watery solution, the latter begins to ooze out in the form of watery drops through the water pore.
