Discuss the experiment and process of unequal transpiration in dicot leaf.

Most of the water absorbed is lost through the aerial parts of the plants into the air by the process called transpiration. Very little water (less than 2%) is used up in various metabolic activities of plants. Most of the transpiration takes place through leaves known as foliar transpiration.

Types of transpiration: Transpiration may occur through the cuticle lenticels stomata and sometimes bark and accordingly it is called Cuticular, lenticular, stomatal, and bark transpiration.

1. Cuticular Transpiration: It is the loss of water in the vapor from the general surface (leaves and young stems) through the layer of the cuticle. Cubicula transpiration is appreciable only in case the cuticle is thin as in entophytic plants growing in humid areas. It is continuous throughout day and night.
   
   
2. Stomatal Transpiration: It is the loss of water in vapor from the stomata present on the surface of leaves and to a lesser extent on the surface of flowers and young stems. It is the major part of transpiration (80-90%) it, however, occurs only when stomata are open.
   
   
3. Lenticular Transpiration: This is the loss of water in vapor from lenticels or aerating poxes present in the bark of stems.
   
   
4. Bark transpiration: A small quantity of water is lost from the corky bark of the stem. Both lenticular and bark transpiration continues day and night time.

Demonstrate the Process of the unequal rate of transpiration in a dorsiventral leaf.

Requirements:

Apparatus: Two glass slides, two clips, filter paper, spirit lamp, and forceps.

Materials: Dorsiventral plant with leaf

Chemical: 5% Cobalt chloride solution, Vaseline

Theory: The rate of transpiration from the two surfaces of the dorsiventral leaf is not the same due to an unequal number of stomata per unit area on the two surfaces.

Procedure: Prepare 5% cobalt chloride solution by dissolving 5mg of anhydrous cobalt chloride into 100ml distilled water. Take a healthy potted plant with an elongated dorsiventral leaf. Wipe the leaf with the help of dry cotton. Take two pieces of filter paper of equal sizes. Soak pieces of filter paper in cobalt chloride solution. The moistened filter paper appears pink in color. Dry the pink-colored filter paper with the help of a spirit lamp until it turns blue. Place a blue filter paper on both the surfaces of the dorsiventral leaf. Cover the pieces of blue filter paper with dry and clean glass slides. Tie slides with clips. Apply Vaseline over the edges of the slide to make it airtight. Place the experimental setup in sunlight and observe continuously.

Observation: The blue color of cobalt chloride paper on the lower surface starts to change into pink color within few minutes while the paper on the upper surface takes some more time to turn into pink color.

Result and Conclusion: The change in color of filter paper on both surfaces of leaf from blue to pink is due to the effect of the moisture which comes out from the leaf. Since the numbers of stomata are more in the lower surface of a leaf, the color of filter paper changes from blue to pink quickly due to vigorous transpiration. On the other hand, the change in color of filter paper on the upper surface of the leaf is slow due to a smaller number of stomata. This concludes the unequal rate of transpiration on the two surfaces of the dorsiventral leaf.

Precautions:

1. The potted plant should be healthy and well-watered.
2. Indicator paper should be in equal size.
3. Moist filter paper should be dried completely.
4. The experimental leaf should be wiped and dried.
5. Vaseline should be applied on the edges of the glass side properly.