(7) Water potential (y)
The movement of water in plants cannot be accurately explained in terms of difference in concentration or in any other linear expression. The best way to express spontaneous movement of water from one region to another is in terms of the difference of free energy of water between two regions. Free energy is the thermodynamic parameter that determines the direction in which physical and chemical changes must occur. The potential energy of water is called water potential. e.g., water is stored behind a dam.
(8) Types of stomata
On the basis of orientation of subsidiary cells around the guard cells, Metcalfe and Chalk classified stomata into following types :
(i) Anomocytic : The guard cells are surrounded by a limited number of unspecialised subsidiary cells which appear similar to other epidermal cells. e.g., in Ranunculaceae family.
(ii) Anisocytic : The guard cells are surrounded by three subsidiary cells, two of which are large and one is very small. e.g., in Solanaceae and Cruciferae families.
(iii) Paracytic : The guard cells are surrounded by only two subsidiary cells lying parallel to the guard cells e.g., Magnoliaceae family.
(iv) Diacytic : The guard cells are surrounded by only two subsidiary cells lying at right angles to the longitudinal axis of the guard cells. e.g., Acanthaceae and Labiatae families.
(v) Actinocytic : The guard cells are surrounded by four or more subsidiary cells and which are elongated radially to stomata.
The movement of water in plants cannot be accurately explained in terms of difference in concentration or in any other linear expression. The best way to express spontaneous movement of water from one region to another is in terms of the difference of free energy of water between two regions. Free energy is the thermodynamic parameter that determines the direction in which physical and chemical changes must occur. The potential energy of water is called water potential. e.g., water is stored behind a dam.
(8) Types of stomata
On the basis of orientation of subsidiary cells around the guard cells, Metcalfe and Chalk classified stomata into following types :
(i) Anomocytic : The guard cells are surrounded by a limited number of unspecialised subsidiary cells which appear similar to other epidermal cells. e.g., in Ranunculaceae family.
(ii) Anisocytic : The guard cells are surrounded by three subsidiary cells, two of which are large and one is very small. e.g., in Solanaceae and Cruciferae families.
(iii) Paracytic : The guard cells are surrounded by only two subsidiary cells lying parallel to the guard cells e.g., Magnoliaceae family.
(iv) Diacytic : The guard cells are surrounded by only two subsidiary cells lying at right angles to the longitudinal axis of the guard cells. e.g., Acanthaceae and Labiatae families.
(v) Actinocytic : The guard cells are surrounded by four or more subsidiary cells and which are elongated radially to stomata.