Water loss in the form of small droplets from hydathodes situated on the tip and margin of leaves is called guttation.
Guttation:
- De Barry (1869) first observed this process.
- Exudation of droplets of water from the tips and margins of leaves is called guttation.
- This loss occurs through minute openings found at the terminal ends of the veins of leaves of some plants.
- These openings are called hydathodes.
- The pore of hydathode is called water pore and is an incompletely differentiated stoma.
- These are permanently open pores because the two cells surrounding the pore are incapable of movement.
- A group of thin-walled loosely arranged parenchyma cells is present below the hydathode.
- This is called epithem.
- The tracheary elements of veins terminate or end just close to the epithem tissue
- When water absorbed by roots exceeds transpiration, root pressure develops and water from xylem vessels and tracheids is pushed in the epithem tissue.
- Finally, water is exuded out in the form of droplets through the pore. Thus guttation is an expression of root pressure.
- Guttation takes place more during the night and early morning hours. Eg. Tomato, grasses, Potato, Bryophyllum, Colocasia etc.
- The fluid lost in guttation is not pure water but contains dissolved minerals and some organic substances also.
- Deposition of minerals and organic substances on the surface of leaves may result in injurious effect and may provide a medium for a pathogenic attack.
