Determination of stomatal number

Stomatal number: It is the average number of stomata per square mm of the epidermis of the leaf.

Procedure:

1. Clear the piece of the leaf (middle part) by boiling with chloral hydrate solution or alternatively with chlorinated soda. Peel out the lower and upper epidermis separately by means of forceps. Keep it on slide and mount in glycerin water.
2. Arrange a camera lucida and drawing board for making the drawings to scale.
3. Draw a square of 1mm by means of stage micrometer.
4. Place the slide with cleared leaf (epidermis) on a stage. Trace the epidermal cell and stomata.
5. Count the number of stomata present in the area of 1 sq mm. Include the cell if at least half of its area lies within the square.
6. Record the result for each of the ten fields and calculate the average number of stomata per sq mm.

	Number of stomata per sq mm
	Upper surface	Lower surface
Cassia auriculata	100-200	130-260
Atropa belladona	7.5- 17.5	77.5- 176
Cassia angustifolia	180-223	195-257

 

The stomatal number is affected by various factors like the age of the plant, the size of the leaf, environmental conditions, etc.

An increase in CO2 decreases stomatal density. Thus, the stomatal number gives an idea of environmental change.

      The number of stomata per unit area increases under more xerophytic conditions.

                

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