“Transpiration is the biological process by which water is LOST in the form of water vapour from the aerial parts of the plants.”

• During the process of transpiration, water molecules in the plant tissues are removed from the aerial parts of the plants.
• Only a small amount of water absorbed by the plants is utilised in growth and development.
• The rest is eliminated in the form of transpiration.

Types of Transpiration

There are three different types of transpiration in plants:

• Stomatal Transpiration

It is the evaporation of water from the stomata of the plants. Most of the water from the plants is transpired this WAY. The water near the surface of the LEAVES changes into vapour and evaporates when the stomata are open.

• Lenticular Transpiration

Lenticels are minute OPENINGS in the bark of branches and twigs. Evaporation of water from the lenticels of the plants is known as lenticular transpiration.

Lenticels are not present in all the plants. A minimal amount of water is lost through lenticels.

• Cuticular Transpiration

It is the evaporation of water from the cuticle of the plants. The cuticle is a waxy covering on the surface of the leaves of the plants. About 5-10% of the water from the leaves is lost through cuticular transpiration. During dry conditions when the stomata are closed, more water is transpired through the cuticles.

Factors Affecting Transpiration in Plants

Different factors affecting the rate of transpiration are:

Cellular Factors

The cellular factors affecting the rate of transpiration are:

• The orientation of leaf,
• The water status of the plant,
• Structural Peculiarities of the leaf,
• Total number and distribution of stomata in a leaf.

Environmental Factors

The environmental factors affecting the rate of transpiration are:

• Light,
• Humidity,
• Temperature,
• Atmospheric pressure,
• Wind speed or velocity.
• Relative Humidity.