Loss of water in plants:
The loss of water in the form the living aerial parts of the plant in the form of water vapour is termed as transpiration. Transpiration is a necessary evil.
It cooled down the leaf surface of plants. Nearly 99% of the water absorbed by the plants is lost in transpiration.
It is a vital and unavoidable phenomenon of plants. Transpiration isregulated by stomata activities.• The principle organ of transpiration is leaf.• Again foliar transpiration is of two types viz. Stomata! (8090 %) and cuticular (up to 20 %).
• These are specialized epidermal cells which are distributed all over leaf surface but in case of terrestrial plants, mainly on lower surface of leaves, therefore approx. 97% of transpiration takes place from the lower surface in such plants.
• Each stomata has two kidney shaped guard cells, inner wall of guard cell is thick and outer wall is thin. Mechanism of stomata opening and closing:
• Opening and closing of stomata are due to its turgidity and flaccidity respectively. Means stomatal movement is governed by Turgor pressure.
• When T.P. of guard cells increases, stomata are opened and when decreases, stomata are closed.
• Rate of transpiration is determined by Photometer.
• Term – Burgerstein,The exudation of water with salt and minerals through hydathode is called Guttation.
• Hydathode: a structure present at tips of veins of leaves. It is caused due to root pressure and Guttation normally occurs at night.